diff --git a/src/common/util/goodies.c b/src/common/util/goodies.c
index 888e725a9..dfaaf53ed 100644
--- a/src/common/util/goodies.c
+++ b/src/common/util/goodies.c
@@ -90,7 +90,7 @@ char *
 space_replace(char * str, char replace)
 {
 	char * c = str;
-	while (*c) {if (isspace(*c)) *c = replace; c++;}
+	while (*c) {if (isspace(*(unsigned char*)c)) *c = replace; c++;}
 	return str;
 }