diff --git a/Source/CParse/cscanner.c b/Source/CParse/cscanner.c
index a3702704e..2113b9cc6 100644
--- a/Source/CParse/cscanner.c
+++ b/Source/CParse/cscanner.c
@@ -93,7 +93,7 @@ int isStructuralDoxygen(String *s) {
     const size_t len = strlen(structuralTags[n]);
     if (strncmp(slashPointer, structuralTags[n], len) == 0) {
       /* Take care to avoid false positives with prefixes of other tags. */
-      if (slashPointer[len] == '\0' || isspace(slashPointer[len]))
+      if (slashPointer[len] == '\0' || isspace((int)slashPointer[len]))
 	return 1;
     }
   }
diff --git a/Source/Preprocessor/cpp.c b/Source/Preprocessor/cpp.c
index 557b5482b..75bec61fd 100644
--- a/Source/Preprocessor/cpp.c
+++ b/Source/Preprocessor/cpp.c
@@ -113,7 +113,7 @@ static int is_digits(const String *str) {
   const char *s = Char(str);
   int isdigits = (*s != 0);
   while (*s) {
-    if (!isdigit(*s)) {
+    if (!isdigit((int)*s)) {
       isdigits = 0;
       break;
     }