diff --git a/cfg/std.cfg b/cfg/std.cfg
index 56831ad1d..047894a4f 100644
--- a/cfg/std.cfg
+++ b/cfg/std.cfg
@@ -1531,6 +1531,7 @@ The obsolete function 'gets' is called. With 'gets' you'll get a buffer overrun
     <pure/>
     <noreturn>false</noreturn>
     <leak-ignore/>
+    <returnValue>arg1==' ' || arg1=='\t'</returnValue>
     <arg nr="1">
       <not-uninit/>
       <valid>0:255</valid>
diff --git a/test/cfg/std.c b/test/cfg/std.c
index b3cde936a..f01c4afc0 100644
--- a/test/cfg/std.c
+++ b/test/cfg/std.c
@@ -3692,7 +3692,7 @@ void valueFlow(void)
 {
     const char abc[] = "abc";
     int three = 3, minusThree = -3;
-    int c0='0', ca='a';
+    int c0='0', ca='a', blank=' ', tab='\t';
 
     // When adding functions below, please sort alphabetically.
 
@@ -3703,7 +3703,21 @@ void valueFlow(void)
     // cppcheck-suppress knownConditionTrueFalse
     AssertAlwaysTrue(abs(minusThree) == 3);
     // cppcheck-suppress knownConditionTrueFalse
+    AssertAlwaysTrue(isblank(blank) == 1);
+    // cppcheck-suppress knownConditionTrueFalse
+    AssertAlwaysTrue(isblank(tab) == 1);
+    // cppcheck-suppress knownConditionTrueFalse
+    AssertAlwaysTrue(isblank(c0) == 0);
+    // cppcheck-suppress knownConditionTrueFalse
     AssertAlwaysTrue(isdigit(c0) == 1);
     // cppcheck-suppress knownConditionTrueFalse
     AssertAlwaysTrue(isdigit(ca) == 0);
+    // cppcheck-suppress knownConditionTrueFalse
+    AssertAlwaysTrue(labs(three) == 3);
+    // cppcheck-suppress knownConditionTrueFalse
+    AssertAlwaysTrue(labs(minusThree) == 3);
+    // cppcheck-suppress knownConditionTrueFalse
+    AssertAlwaysTrue(llabs(three) == 3);
+    // cppcheck-suppress knownConditionTrueFalse
+    AssertAlwaysTrue(llabs(minusThree) == 3);
 }