diff --git a/src/regexp.h b/src/regexp.h
index 5762338..a8bc822 100644
--- a/src/regexp.h
+++ b/src/regexp.h
@@ -31,7 +31,7 @@
  * In the NFA engine: how many states are allowed
  */
 #define NFA_MAX_STATES 100000
-#define NFA_TOO_EXPENSIVE -1
+#define NFA_TOO_EXPENSIVE (-1)
 
 // Which regexp engine to use? Needed for vim_regcomp().
 // Must match with 'regexpengine'.