diff --git a/wand/mogrify.c b/wand/mogrify.c
index 80bf1bf..815bac6 100644
--- a/wand/mogrify.c
+++ b/wand/mogrify.c
@@ -8050,7 +8050,7 @@
                 */
                 length=strlen(argv[i+1]);
                 token=(char *) NULL;
-                if (~length >= MaxTextExtent)
+                if (~length >= (MaxTextExtent-1))
                   token=(char *) AcquireQuantumMemory(length+MaxTextExtent,
                     sizeof(*token));
                 if (token == (char *) NULL)