1 files changed, 6 insertions, 0 deletions
diff --git a/Source/cmSystemTools.cxx b/Source/cmSystemTools.cxx
index d20106128a..212608d489 100644
--- a/Source/cmSystemTools.cxx
+++ b/Source/cmSystemTools.cxx
@@ -3023,6 +3023,12 @@ bool cmSystemTools::StringToULong(const char* str, unsigned long* value)
 {
   errno = 0;
   char* endp;
+  while (isspace(*str)) {
+    ++str;
+  }
+  if (*str == '-') {
+    return false;
+  }
   *value = strtoul(str, &endp, 10);
   return (*endp == '\0') && (endp != str) && (errno == 0);
 }