diff --git a/Source/kwsys/ProcessUNIX.c b/Source/kwsys/ProcessUNIX.c
index 871a53e000..81f0643d4e 100644
--- a/Source/kwsys/ProcessUNIX.c
+++ b/Source/kwsys/ProcessUNIX.c
@@ -2807,7 +2807,7 @@ static char** kwsysProcessParseVerbatimCommand(const char* command)
           }
         }
       }
-    else if(isspace(*c))
+    else if(isspace((int) *c))
       {
       if(in_argument)
         {