diff --git a/inertia.c b/inertia.c
index c0c383a..213ad35 100644
--- a/inertia.c
+++ b/inertia.c
@@ -11,6 +11,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
+#include <limits.h>
 #include <math.h>
 
 #include "puzzles.h"
@@ -202,6 +203,8 @@ static const char *validate_params(const game_params *params, bool full)
      */
     if (params->w < 2 || params->h < 2)
 	return "Width and height must both be at least two";
+    if (params->w > INT_MAX / params->h)
+        return "Width times height must not be unreasonably large";
 
     /*
      * The grid construction algorithm creates 1/5 as many gems as