diff --git a/libs/libc/string/lib_strsep.c b/libs/libc/string/lib_strsep.c
index e30b14cd1cd..3ba681d564e 100644
--- a/libs/libc/string/lib_strsep.c
+++ b/libs/libc/string/lib_strsep.c
@@ -66,7 +66,7 @@ FAR char *strsep(FAR char **strp, FAR const char *delim)
   FAR char *sbegin = *strp;
   FAR char *end;
 
-  if !sbegin == NULL)
+  if (sbegin == NULL)
     {
       return NULL;
     }