diff --git a/flood.c b/flood.c
index eeca88b..67181a8 100644
--- a/flood.c
+++ b/flood.c
@@ -31,6 +31,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
+#include <limits.h>
 #include <math.h>
 
 #include "puzzles.h"
@@ -209,6 +210,8 @@ static const char *validate_params(const game_params *params, bool full)
 {
     if (params->w < 2 && params->h < 2)
         return "Grid must contain at least two squares";
+    if (params->w > INT_MAX / params->h)
+        return "Width times height must not be unreasonably large";
     if (params->colours < 3 || params->colours > 10)
         return "Must have between 3 and 10 colours";
     if (params->leniency < 0)