diff --git a/ChangeLog b/ChangeLog
index 19e0230..5678765 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -79,6 +79,9 @@ copied).
       pattern one further code unit was read.
       
   (h) An unterminated number after \g' could cause reading beyond the pattern. 
+  
+  (i) An insufficient memory size was being computed for compiling with 
+      PCRE2_AUTO_CALLOUT. 
 
 4. Back references are now permitted in lookbehind assertions when there are 
 no duplicated group numbers (that is, (?| has not been used), and, if the 
diff --git a/src/pcre2_compile.c b/src/pcre2_compile.c
index 850ba7b..2519147 100644
--- a/src/pcre2_compile.c
+++ b/src/pcre2_compile.c
@@ -2146,6 +2146,7 @@ uint32_t class_range_state;
 uint32_t *verblengthptr = NULL;     /* Value avoids compiler warning */
 uint32_t *previous_callout = NULL;
 uint32_t *parsed_pattern = cb->parsed_pattern;
+uint32_t *parsed_pattern_end = cb->parsed_pattern_end;
 uint32_t meta_quantifier = 0;
 uint16_t nest_depth = 0;
 int after_manual_callout = 0;
@@ -2188,6 +2189,12 @@ while (ptr < ptrend)
   PCRE2_SPTR tempptr;
   PCRE2_SPTR thisptr;
   PCRE2_SIZE offset;
+  
+  if (parsed_pattern >= parsed_pattern_end)
+    {
+    errorcode = ERR63;  /* Internal error (parsed pattern overflow) */
+    goto FAILED; 
+    }   
 
   if (nest_depth > cb->cx->parens_nest_limit)
     {
@@ -9158,7 +9165,7 @@ used. */
 
 parsed_size_needed = patlen - skipatstart + big32count;
 if ((options & PCRE2_AUTO_CALLOUT) != 0)
-  parsed_size_needed = (parsed_size_needed + 1) * 4;
+  parsed_size_needed = (parsed_size_needed + 1) * 5;
 
 if (parsed_size_needed >= PARSED_PATTERN_DEFAULT_SIZE)
   {
@@ -9171,7 +9178,8 @@ if (parsed_size_needed >= PARSED_PATTERN_DEFAULT_SIZE)
     }
   cb.parsed_pattern = heap_parsed_pattern;
   }
-
+cb.parsed_pattern_end = cb.parsed_pattern + parsed_size_needed + 1; 
+  
 /* Do the parsing scan. */
 
 errorcode = parse_regex(ptr, cb.external_options, &has_lookbehind, &cb);
diff --git a/src/pcre2_error.c b/src/pcre2_error.c
index c09d3d9..83c647d 100644
--- a/src/pcre2_error.c
+++ b/src/pcre2_error.c
@@ -138,7 +138,7 @@ static const unsigned char compile_error_texts[] =
   "(*VERB) not recognized or malformed\0"
   "group number is too big\0"
   "subpattern name expected\0"
-  "SPARE ERROR\0"
+  "internal error: parsed pattern overflow\0"
   "non-octal character in \\o{} (closing brace missing?)\0"
   /* 65 */
   "different names for subpatterns of the same number are not allowed\0"
diff --git a/src/pcre2_fuzzsupport.c b/src/pcre2_fuzzsupport.c
index 2c0e56a..ef52908 100644
--- a/src/pcre2_fuzzsupport.c
+++ b/src/pcre2_fuzzsupport.c
@@ -65,11 +65,11 @@ reason to disallow UTF and UCP. Force PCRE2_NEVER_BACKSLASH_C to be set because
 \C in random patterns is highly likely to cause a crash.  */
 
 compile_options =
-  ((uint32_t)((r1 << 16) | (r2 & 0xffff)) & ALLOWED_COMPILE_OPTIONS) |
+  ((((uint32_t)r1 << 16) | ((uint32_t)r2 & 0xffff)) & ALLOWED_COMPILE_OPTIONS) |
   PCRE2_NEVER_BACKSLASH_C;
 
 match_options =
-  ((uint32_t)((r1 << 16) | (r2 & 0xffff)) & ALLOWED_MATCH_OPTIONS);
+  ((((uint32_t)r1 << 16) | ((uint32_t)r2 & 0xffff)) & ALLOWED_MATCH_OPTIONS);
 
 /* Do the compile with and without the options, and after a successful compile,
 likewise do the match with and without the options. */
diff --git a/src/pcre2_intmodedep.h b/src/pcre2_intmodedep.h
index 0579bd6..843204b 100644
--- a/src/pcre2_intmodedep.h
+++ b/src/pcre2_intmodedep.h
@@ -713,6 +713,7 @@ typedef struct compile_block {
   uint32_t bracount;               /* Count of capturing parentheses */
   uint32_t lastcapture;            /* Last capture encountered */ 
   uint32_t *parsed_pattern;        /* Parsed pattern buffer */ 
+  uint32_t *parsed_pattern_end;    /* Parsed pattern should not get here */ 
   uint32_t *groupinfo;             /* Group info vector */
   uint32_t top_backref;            /* Maximum back reference */
   uint32_t backref_map;            /* Bitmap of low back refs */