diff --git a/ChangeLog b/ChangeLog
index f3e1cc5..c6d3480 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -77,6 +77,10 @@ whose condition was an assertion preceded by an explicit callout with a string
 argument might be incorrectly processed, especially if the string contained \Q.
 This bug was discovered by Karl Skomski with the LLVM fuzzer.
 
+21. Compiling PCRE2 with the sanitize options of clang showed up a number of 
+very pedantic coding infelicities and a buffer overflow while checking a UTF-8 
+string if the final multi-byte UTF-8 character was truncated.
+
 
 Version 10.20 30-June-2015
 --------------------------
diff --git a/RunTest b/RunTest
index c4d659c..fb758fe 100755
--- a/RunTest
+++ b/RunTest
@@ -33,6 +33,10 @@
 # For backwards compatibility, -nojit, -valgrind, -valgrind-log, and -sim may
 # be given without the leading "-" character.
 #
+# When PCRE2 is compiled by clang with -fsanitize arguments, some tests need
+# very much more stack than normal. In environments where the stack can be
+# set at runtime, -bigstack sets a gigantic stack.
+#
 # There are two special cases where only one argument is allowed:
 #
 # If the first and only argument is "ebcdic", the script runs the special
@@ -184,6 +188,7 @@ arg8=
 arg16=
 arg32=
 nojit=
+bigstack=
 sim=
 skip=
 valgrind=
@@ -240,6 +245,7 @@ while [ $# -gt 0 ] ; do
    -8) arg8=yes;;
   -16) arg16=yes;;
   -32) arg32=yes;;
+   bigstack|-bigstack) bigstack=yes;; 
    nojit|-nojit) nojit=yes;;
    sim|-sim) shift; sim=$1;;
    valgrind|-valgrind) valgrind="valgrind --tool=memcheck -q --smc-check=all";;
@@ -287,13 +293,22 @@ fi
 
 # If it is possible to set the system stack size, arrange to set a value for
 # test 2, which needs more than the even the Linux default when PCRE2 has been
-# compiled with -fsanitize=address.
+# compiled by gcc with -fsanitize=address. When the compiler is clang, sanitize
+# options require an even bigger stack for test 2, and an increased stack for
+# some of the other tests.
 
 $sim ./pcre2test -S 1 /dev/null /dev/null
 if [ $? -eq 0 ] ; then
-  test2stack="-S 16"
+  if [ "$bigstack" = "" ] ; then
+    test2stack="-S 16"
+    defaultstack=""
+  else
+    test2stack="-S 1024"
+    defaultstack="-S 64"
+  fi         
 else
   test2stack=""
+  defaultstack="" 
 fi
 
 # All of 8-bit, 16-bit, and 32-bit character strings may be supported, but only
@@ -438,7 +453,7 @@ for bmode in "$test8" "$test16" "$test32"; do
   if [ $do1 = yes ] ; then
     echo $title1
     for opt in "" $jitopt; do
-      $sim $valgrind ./pcre2test -q $bmode $opt $testdata/testinput1 testtry
+      $sim $valgrind ./pcre2test -q $defaultstack $bmode $opt $testdata/testinput1 testtry
       checkresult $? 1 "$opt"
     done
   fi
@@ -508,7 +523,7 @@ for bmode in "$test8" "$test16" "$test32"; do
     if [ "$locale" != "" ] ; then
       echo $title3 "(using '$locale' locale)"
       for opt in "" $jitopt; do
-        $sim $valgrind ./pcre2test -q $bmode $opt $infile testtry
+        $sim $valgrind ./pcre2test -q $defaultstack $bmode $opt $infile testtry
         if [ $? = 0 ] ; then
           case "$opt" in
             -jit) with=" with JIT";;
@@ -545,7 +560,7 @@ for bmode in "$test8" "$test16" "$test32"; do
       echo "  Skipped because UTF-$bits support is not available"
     else
       for opt in "" $jitopt; do
-        $sim $valgrind ./pcre2test -q $bmode $opt $testdata/testinput4 testtry
+        $sim $valgrind ./pcre2test -q $defaultstack $bmode $opt $testdata/testinput4 testtry
         checkresult $? 4 "$opt"
       done
     fi
@@ -557,7 +572,7 @@ for bmode in "$test8" "$test16" "$test32"; do
       echo "  Skipped because UTF-$bits support is not available"
     else
       for opt in "" $jitopt; do
-        $sim $valgrind ./pcre2test -q $bmode $opt $testdata/testinput5 testtry
+        $sim $valgrind ./pcre2test -q $defaultstack $bmode $opt $testdata/testinput5 testtry
         checkresult $? 5 "$opt"
       done
     fi
@@ -567,7 +582,7 @@ for bmode in "$test8" "$test16" "$test32"; do
 
   if [ $do6 = yes ] ; then
     echo $title6
-    $sim $valgrind ./pcre2test -q $bmode $testdata/testinput6 testtry
+    $sim $valgrind ./pcre2test -q $defaultstack $bmode $testdata/testinput6 testtry
     checkresult $? 6 ""
   fi
 
@@ -576,7 +591,7 @@ for bmode in "$test8" "$test16" "$test32"; do
     if [ $utf -eq 0 ] ; then
       echo "  Skipped because UTF-$bits support is not available"
     else
-      $sim $valgrind ./pcre2test -q $bmode $opt $testdata/testinput7 testtry
+      $sim $valgrind ./pcre2test -q $defaultstack $bmode $opt $testdata/testinput7 testtry
       checkresult $? 7 ""
     fi
   fi
@@ -596,7 +611,7 @@ for bmode in "$test8" "$test16" "$test32"; do
     elif [ $utf -eq 0 ] ; then
       echo "  Skipped because UTF-$bits support is not available"
     else
-      $sim $valgrind ./pcre2test -q $bmode $testdata/testinput8 testtry
+      $sim $valgrind ./pcre2test -q $defaultstack $bmode $testdata/testinput8 testtry
       checkresult $? 8-$bits ""
     fi
   fi
@@ -609,7 +624,7 @@ for bmode in "$test8" "$test16" "$test32"; do
       echo "  Skipped when running 16/32-bit tests"
     else
       for opt in "" $jitopt; do
-        $sim $valgrind ./pcre2test -q $bmode $opt $testdata/testinput9 testtry
+        $sim $valgrind ./pcre2test -q $defaultstack $bmode $opt $testdata/testinput9 testtry
         checkresult $? 9 "$opt"
       done
     fi
@@ -625,7 +640,7 @@ for bmode in "$test8" "$test16" "$test32"; do
       echo "  Skipped because UTF-$bits support is not available"
     else
       for opt in "" $jitopt; do
-        $sim $valgrind ./pcre2test -q $bmode $opt $testdata/testinput10 testtry
+        $sim $valgrind ./pcre2test -q $defaultstack $bmode $opt $testdata/testinput10 testtry
         checkresult $? 10 "$opt"
       done
     fi
@@ -639,7 +654,7 @@ for bmode in "$test8" "$test16" "$test32"; do
       echo "  Skipped when running 8-bit tests"
     else
       for opt in "" $jitopt; do
-        $sim $valgrind ./pcre2test -q $bmode $opt $testdata/testinput11 testtry
+        $sim $valgrind ./pcre2test -q $defaultstack $bmode $opt $testdata/testinput11 testtry
         checkresult $? 11-$bits "$opt"
       done
     fi
@@ -656,7 +671,7 @@ for bmode in "$test8" "$test16" "$test32"; do
       echo "  Skipped because UTF-$bits support is not available"
     else
       for opt in "" $jitopt; do
-        $sim $valgrind ./pcre2test -q $bmode $opt $testdata/testinput12 testtry
+        $sim $valgrind ./pcre2test -q $defaultstack $bmode $opt $testdata/testinput12 testtry
         checkresult $? 12-$bits "$opt"
       done
     fi
@@ -669,7 +684,7 @@ for bmode in "$test8" "$test16" "$test32"; do
     if [ "$bits" = "8" ] ; then
       echo "  Skipped when running 8-bit tests"
     else
-      $sim $valgrind ./pcre2test -q $bmode $testdata/testinput13 testtry
+      $sim $valgrind ./pcre2test -q $defaultstack $bmode $testdata/testinput13 testtry
       checkresult $? 13 ""
     fi
   fi
@@ -678,7 +693,7 @@ for bmode in "$test8" "$test16" "$test32"; do
 
   if [ $do14 = yes ] ; then
     echo $title14
-    $sim $valgrind ./pcre2test -q $bmode $testdata/testinput14 testtry
+    $sim $valgrind ./pcre2test -q $defaultstack $bmode $testdata/testinput14 testtry
     checkresult $? 14 ""
   fi
 
@@ -689,7 +704,7 @@ for bmode in "$test8" "$test16" "$test32"; do
     if [ $jit -ne 0 ] ; then
       echo "  Skipped because JIT is available"
     else
-      $sim $valgrind ./pcre2test -q $bmode $testdata/testinput15 testtry
+      $sim $valgrind ./pcre2test -q $defaultstack $bmode $testdata/testinput15 testtry
       checkresult $? 15 ""
     fi
   fi
@@ -701,7 +716,7 @@ for bmode in "$test8" "$test16" "$test32"; do
     if [ $jit -eq 0 -o "$nojit" = "yes" ] ; then
       echo "  Skipped because JIT is not available or nojit was specified"
     else
-      $sim $valgrind ./pcre2test -q $bmode $testdata/testinput16 testtry
+      $sim $valgrind ./pcre2test -q $defaultstack $bmode $testdata/testinput16 testtry
       checkresult $? 16 ""
     fi
   fi
@@ -713,7 +728,7 @@ for bmode in "$test8" "$test16" "$test32"; do
     if [ "$bits" = "16" -o "$bits" = "32" ] ; then
       echo "  Skipped when running 16/32-bit tests"
     else
-      $sim $valgrind ./pcre2test -q $bmode $testdata/testinput17 testtry
+      $sim $valgrind ./pcre2test -q $defaultstack $bmode $testdata/testinput17 testtry
       checkresult $? 17 ""
     fi
   fi
@@ -727,7 +742,7 @@ for bmode in "$test8" "$test16" "$test32"; do
     elif [ $utf -eq 0 ] ; then
       echo "  Skipped because UTF-$bits support is not available"
     else
-      $sim $valgrind ./pcre2test -q $bmode $testdata/testinput18 testtry
+      $sim $valgrind ./pcre2test -q $defaultstack $bmode $testdata/testinput18 testtry
       checkresult $? 18 ""
     fi
   fi
@@ -736,7 +751,7 @@ for bmode in "$test8" "$test16" "$test32"; do
 
   if [ $do19 = yes ] ; then
     echo $title19
-    $sim $valgrind ./pcre2test -q $bmode $testdata/testinput19 testtry
+    $sim $valgrind ./pcre2test -q $defaultstack $bmode $testdata/testinput19 testtry
     checkresult $? 19 ""
   fi
 
diff --git a/src/pcre2_compile.c b/src/pcre2_compile.c
index 5fe9440..08ea585 100644
--- a/src/pcre2_compile.c
+++ b/src/pcre2_compile.c
@@ -270,7 +270,7 @@ in UTF-8 mode. It runs from '0' to 'z'. */
 #ifndef EBCDIC
 #define ESCAPES_FIRST       CHAR_0
 #define ESCAPES_LAST        CHAR_z
-#define ESCAPES_UPPER_CASE  (-32)    /* Add this to upper case a letter */
+#define UPPER_CASE(c)       (c-32)
 
 static const short int escapes[] = {
      0,                       0,
@@ -323,11 +323,11 @@ because it is defined as 'a', which of course picks up the ASCII value. */
 #if 'a' == 0x81                    /* Check for a real EBCDIC environment */
 #define ESCAPES_FIRST       CHAR_a
 #define ESCAPES_LAST        CHAR_9
-#define ESCAPES_UPPER_CASE  (+64)  /* Add this to upper case a letter */
+#define UPPER_CASE(c)       (c+64)
 #else                              /* Testing in an ASCII environment */
 #define ESCAPES_FIRST  ((unsigned char)'\x81')   /* EBCDIC 'a' */
 #define ESCAPES_LAST   ((unsigned char)'\xf9')   /* EBCDIC '9' */
-#define ESCAPES_UPPER_CASE  (-32)  /* Add this to upper case a letter */
+#define UPPER_CASE(c)  (c-32)
 #endif
 
 static const short int escapes[] = {
@@ -1884,7 +1884,7 @@ else
       s = cb->bracount - (s - 1);
       }
 
-    escape = -s;
+    escape = -(int)s;
     break;
 
     /* The handling of escape sequences consisting of a string of digits
@@ -1909,7 +1909,7 @@ else
       {
       oldptr = ptr;
       /* The integer range is limited by the machine's int representation. */
-      s = (int)(c - CHAR_0);
+      s = c - CHAR_0;
       overflow = FALSE;
       while (IS_DIGIT(ptr[1]))
         {
@@ -1933,7 +1933,7 @@ else
 
       if (s < 10 || *oldptr >= CHAR_8 || s <= cb->bracount)
         {
-        escape = -s;     /* Indicates a back reference */
+        escape = -(int)s;     /* Indicates a back reference */
         break;
         }
       ptr = oldptr;      /* Put the pointer back and fall through */
@@ -1981,7 +1981,7 @@ else
 #if PCRE2_CODE_UNIT_WIDTH == 32
         if (c >= 0x20000000l) { overflow = TRUE; break; }
 #endif
-        c = (c << 3) + cc - CHAR_0 ;
+        c = (c << 3) + (cc - CHAR_0);
 #if PCRE2_CODE_UNIT_WIDTH == 8
         if (c > (utf ? 0x10ffffU : 0xffU)) { overflow = TRUE; break; }
 #elif PCRE2_CODE_UNIT_WIDTH == 16
@@ -2105,7 +2105,7 @@ else
 #endif
 
     c = *(++ptr);
-    if (c >= CHAR_a && c <= CHAR_z) c += ESCAPES_UPPER_CASE;
+    if (c >= CHAR_a && c <= CHAR_z) c = UPPER_CASE(c);
     if (c == CHAR_NULL && ptr >= cb->end_pattern)
       {
       *errorcodeptr = ERR2;
@@ -3532,7 +3532,7 @@ for (; ptr < cb->end_pattern; ptr++)
       if (top_nest == (nest_save *)(cb->start_workspace)) top_nest = NULL;
         else top_nest--;
       }
-    nest_depth--;
+    if (nest_depth > 0) nest_depth--;  /* Can be 0 for unmatched ) */
     break;
     }
   }
@@ -3938,14 +3938,16 @@ for (;; ptr++)
     if (PRIV(strncmp_c8)(ptr+1, STRING_WEIRD_STARTWORD, 6) == 0)
       {
       nestptr = ptr + 7;
-      ptr = sub_start_of_word - 1;
+      ptr = sub_start_of_word;  /* Do not combine these statements; clang's */
+      ptr--;                    /* sanitizer moans about a negative index. */ 
       continue;
       }
 
     if (PRIV(strncmp_c8)(ptr+1, STRING_WEIRD_ENDWORD, 6) == 0)
       {
       nestptr = ptr + 7;
-      ptr = sub_end_of_word - 1;
+      ptr = sub_end_of_word;    /* Do not combine these statements; clang's */
+      ptr--;                    /* sanitizer moans about a negative index. */ 
       continue;
       }
 
@@ -5960,7 +5962,7 @@ for (;; ptr++)
             goto FAILED;
             }
           if (refsign != 0) recno = (refsign == CHAR_MINUS)?
-            cb->bracount - recno + 1 : recno + cb->bracount;
+            (cb->bracount + 1) - recno : recno + cb->bracount;
           if (recno <= 0 || (uint32_t)recno > cb->final_bracount)
             {
             *errorcodeptr = ERR15;
@@ -6490,7 +6492,7 @@ for (;; ptr++)
               *errorcodeptr = ERR58;
               goto FAILED;
               }
-            recno = cb->bracount - recno + 1;
+            recno = (int)(cb->bracount + 1) - recno;
             if (recno <= 0)
               {
               *errorcodeptr = ERR15;
@@ -8183,7 +8185,7 @@ while (ptr[skipatstart] == CHAR_LEFT_PARENTHESIS &&
         while (IS_DIGIT(ptr[pp]))
           {
           if (c > UINT32_MAX / 10 - 1) break;   /* Integer overflow */
-          c = c*10 + ptr[pp++] - CHAR_0;
+          c = c*10 + (ptr[pp++] - CHAR_0);
           }
         if (ptr[pp++] != CHAR_RIGHT_PARENTHESIS)
           {
diff --git a/src/pcre2_dfa_match.c b/src/pcre2_dfa_match.c
index b14477d..ff4d332 100644
--- a/src/pcre2_dfa_match.c
+++ b/src/pcre2_dfa_match.c
@@ -3172,7 +3172,7 @@ occur. */
 
 #define FF (PCRE2_NOTEMPTY_SET|PCRE2_NE_ATST_SET)
 #define OO (PCRE2_NOTEMPTY|PCRE2_NOTEMPTY_ATSTART)
-options |= (re->flags & FF) / ((FF & -FF) / (OO & -OO));
+options |= (re->flags & FF) / ((FF & (~FF+1)) / (OO & (~OO+1)));
 #undef FF
 #undef OO
 
diff --git a/src/pcre2_match.c b/src/pcre2_match.c
index 5d3e694..41113a5 100644
--- a/src/pcre2_match.c
+++ b/src/pcre2_match.c
@@ -194,7 +194,7 @@ if (caseless)
       GETCHARINC(c, eptr);
       GETCHARINC(d, p);
       ur = GET_UCD(d);
-      if (c != d && c != d + ur->other_case)
+      if (c != d && c != (uint32_t)((int)d + ur->other_case))
         {
         const uint32_t *pp = PRIV(ucd_caseless_sets) + ur->caseset;
         for (;;)
@@ -211,7 +211,7 @@ if (caseless)
     /* Not in UTF mode */
 
     {
-    while (length-- > 0)
+    for (; length > 0; length--)
       {
       uint32_t cc, cp;
       if (eptr >= mb->end_subject) return 1;   /* Partial match */
@@ -226,11 +226,11 @@ if (caseless)
   }
 
 /* In the caseful case, we can just compare the code units, whether or not we
-are in UT mode. */
+are in UTF mode. */
 
 else
   {
-  while (length-- > 0)
+  for (; length > 0; length--)
     {
     if (eptr >= mb->end_subject) return 1;   /* Partial match */
     if (UCHAR21INCTEST(p) != UCHAR21INCTEST(eptr)) return -1;  /*No match */
@@ -3342,7 +3342,10 @@ for (;;)
         CHECK_PARTIAL();             /* Not SCHECK_PARTIAL() */
         RRETURN(MATCH_NOMATCH);
         }
-      while (length-- > 0) if (*ecode++ != UCHAR21INC(eptr)) RRETURN(MATCH_NOMATCH);
+      for (; length > 0; length--)
+        {
+        if (*ecode++ != UCHAR21INC(eptr)) RRETURN(MATCH_NOMATCH);
+        }
       }
     else
 #endif
@@ -6513,7 +6516,7 @@ occur. */
 
 #define FF (PCRE2_NOTEMPTY_SET|PCRE2_NE_ATST_SET)
 #define OO (PCRE2_NOTEMPTY|PCRE2_NOTEMPTY_ATSTART)
-options |= (re->flags & FF) / ((FF & -FF) / (OO & -OO));
+options |= (re->flags & FF) / ((FF & (~FF+1)) / (OO & (~OO+1)));
 #undef FF
 #undef OO
 
@@ -6783,7 +6786,7 @@ for(;;)
       end_subject = t;
       }
 
-    /* Advance to a unique first code unit if there is one. In 8-bit mode, the 
+    /* Advance to a unique first code unit if there is one. In 8-bit mode, the
     use of memchr() gives a big speed up. */
 
     if (has_first_cu)
@@ -6801,8 +6804,8 @@ for(;;)
 #else
         start_match = memchr(start_match, first_cu, end_subject - start_match);
         if (start_match == NULL) start_match = end_subject;
-#endif          
-        }   
+#endif
+        }
       }
 
     /* Or to just after a linebreak for a multiline match */
diff --git a/src/pcre2_string_utils.c b/src/pcre2_string_utils.c
index 888620e..1962cf3 100644
--- a/src/pcre2_string_utils.c
+++ b/src/pcre2_string_utils.c
@@ -121,7 +121,7 @@ int
 PRIV(strncmp)(PCRE2_SPTR str1, PCRE2_SPTR str2, size_t len)
 {
 PCRE2_UCHAR c1, c2;
-while (len-- > 0)
+for (; len > 0; len--)
   {
   c1 = *str1++;
   c2 = *str2++;
@@ -150,7 +150,7 @@ int
 PRIV(strncmp_c8)(PCRE2_SPTR str1, const char *str2, size_t len)
 {
 PCRE2_UCHAR c1, c2;
-while (len-- > 0)
+for (; len > 0; len--)
   {
   c1 = *str1++;
   c2 = *str2++;
diff --git a/src/pcre2_valid_utf.c b/src/pcre2_valid_utf.c
index a97847a..94e97d7 100644
--- a/src/pcre2_valid_utf.c
+++ b/src/pcre2_valid_utf.c
@@ -131,11 +131,13 @@ PCRE2_ERROR_UTF8_ERR20  Isolated 0x80 byte (not within UTF-8 character)
 PCRE2_ERROR_UTF8_ERR21  Byte with the illegal value 0xfe or 0xff
 */
 
-for (p = string; length-- > 0; p++)
+for (p = string; length > 0; p++)
   {
   register uint32_t ab, d;
 
   c = *p;
+  length--; 
+
   if (c < 128) continue;                /* ASCII character */
 
   if (c < 0xc0)                         /* Isolated 10xx xxxx byte */
@@ -324,9 +326,10 @@ PCRE2_ERROR_UTF16_ERR2  Invalid low surrogate
 PCRE2_ERROR_UTF16_ERR3  Isolated low surrogate
 */
 
-for (p = string; length-- > 0; p++)
+for (p = string; length > 0; p++)
   {
   c = *p;
+  length--; 
 
   if ((c & 0xf800) != 0xd800)
     {
@@ -368,7 +371,7 @@ PCRE2_ERROR_UTF32_ERR1  Surrogate character
 PCRE2_ERROR_UTF32_ERR2  Character > 0x10ffff
 */
 
-for (p = string; length-- > 0; p++)
+for (p = string; length > 0; length--, p++)
   {
   c = *p;
   if ((c & 0xfffff800u) != 0xd800u)
diff --git a/src/pcre2test.c b/src/pcre2test.c
index 43a056a..540b53e 100644
--- a/src/pcre2test.c
+++ b/src/pcre2test.c
@@ -2606,7 +2606,7 @@ if (pbuffer16_size < 2*len + 2)
 pp = pbuffer16;
 if (!utf)
   {
-  while (len-- > 0) *pp++ = *p++;
+  for (; len > 0; len--) *pp++ = *p++;
   }
 else while (len > 0)
   {
@@ -2683,7 +2683,7 @@ if (pbuffer32_size < 4*len + 4)
 pp = pbuffer32;
 if (!utf)
   {
-  while (len-- > 0) *pp++ = *p++;
+  for (; len > 0; len--) *pp++ = *p++;
   }
 else while (len > 0)
   {
@@ -2723,9 +2723,8 @@ Returns:   a possibly changed offset
 static PCRE2_SIZE
 backchars(uint8_t *subject, PCRE2_SIZE offset, uint32_t count, BOOL utf)
 {
-long int yield;
-
-if (!utf || test_mode == PCRE32_MODE) yield = offset - count;
+if (!utf || test_mode == PCRE32_MODE)
+  return (count >= offset)? 0 : (offset - count);
 
 else if (test_mode == PCRE8_MODE)
   {
@@ -2735,7 +2734,7 @@ else if (test_mode == PCRE8_MODE)
     pp--;
     while ((*pp & 0xc0) == 0x80) pp--;
     }
-  yield = pp - (PCRE2_SPTR8)subject;
+  return pp - (PCRE2_SPTR8)subject;
   }
 
 else  /* 16-bit mode */
@@ -2746,10 +2745,8 @@ else  /* 16-bit mode */
     pp--;
     if ((*pp & 0xfc00) == 0xdc00) pp--;
     }
-  yield = pp - (PCRE2_SPTR16)subject;
+  return pp - (PCRE2_SPTR16)subject;
   }
-
-return (yield >= 0)? yield : 0;
 }
 
 
@@ -2936,7 +2933,7 @@ while (top > bot)
   if (c == 0)
     {
     if (len == mlen) return mid;
-    c = len - mlen;
+    c = (int)len - (int)mlen;
     }
   if (c > 0) bot = mid + 1; else top = mid;
   }
@@ -3712,7 +3709,7 @@ if ((pat_patctl.control & CTL_INFO) != 0)
   if (namecount > 0)
     {
     fprintf(outfile, "Named capturing subpatterns:\n");
-    while (namecount-- > 0)
+    for (; namecount > 0; namecount--)
       {
       int imm2_size = test_mode == PCRE8_MODE ? 2 : 1;
       uint32_t length = (uint32_t)STRLEN(nametable + imm2_size);
@@ -5378,7 +5375,7 @@ if (p[-1] != 0 && !decode_modifiers(p, CTX_DAT, NULL, &dat_datctl))
 /* Check for mutually exclusive modifiers. */
 
 c = dat_datctl.control & EXCLUSIVE_DAT_CONTROLS;
-if (c - (c & -c) != 0)
+if (c != 0 && c != (c & (~c+1)))
   {
   show_controls(c, "** Not allowed together:");
   fprintf(outfile, "\n");