From c01495f91ac71c5205f52713430b68e80d851149 Mon Sep 17 00:00:00 2001
From: Cristy <urban-warrior@imagemagick.org>
Date: Sat, 5 Oct 2019 08:56:29 -0400
Subject: [PATCH] https://github.com/ImageMagick/ImageMagick/issues/1721

---
 magick/string.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/magick/string.c b/magick/string.c
index f6f7b9318..1b47f562e 100644
--- a/magick/string.c
+++ b/magick/string.c
@@ -2534,7 +2534,7 @@ MagickExport MagickBooleanType SubstituteString(char **string,
   {
     if (search_extent == 0)
       search_extent=strlen(search);
-    if (strncmp(p,search,search_extent) != 0)
+    if ((*p == *search) && (strncmp(p,search,search_extent) != 0))
       continue;
     /*
       We found a match.
@@ -2562,7 +2562,9 @@ MagickExport MagickBooleanType SubstituteString(char **string,
       (void) memmove(p+replace_extent,p+search_extent,
         strlen(p+search_extent)+1);
     (void) memcpy(p,replace,replace_extent);
-    p+=replace_extent-1;
+    p+=replace_extent;
+    if (replace_extent != 0)
+      p--;
   }
   return(status);
 }