diff --git a/src/fold.c b/src/fold.c
index 4b4e618..82ce7e7 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -640,7 +640,10 @@
 		break;
 	    }
 	}
-	i = (int)(fp - (fold_T *)gap->ga_data);
+	if (gap->ga_len == 0)
+	    i = 0;
+	else
+	    i = (int)(fp - (fold_T *)gap->ga_data);
     }
 
     if (ga_grow(gap, 1) == OK)