1 files changed, 2 insertions, 2 deletions
diff --git a/ext/json/generator/generator.c b/ext/json/generator/generator.c
index 42a1658811..7bc193455d 100644
--- a/ext/json/generator/generator.c
+++ b/ext/json/generator/generator.c
@@ -894,8 +894,8 @@ static int isArrayOrObject(VALUE string)
     long string_len = RSTRING_LEN(string);
     char *p = RSTRING_PTR(string), *q = p + string_len - 1;
     if (string_len < 2) return 0;
-    for (; p < q && isspace(*p); p++);
-    for (; q > p && isspace(*q); q--);
+    for (; p < q && isspace((unsigned char)*p); p++);
+    for (; q > p && isspace((unsigned char)*q); q--);
     return (*p == '[' && *q == ']') || (*p == '{' && *q == '}');
 }