diff --git a/OpenCL/inc_rp.cl b/OpenCL/inc_rp.cl
index 1d17b365e..2e4d43a85 100644
--- a/OpenCL/inc_rp.cl
+++ b/OpenCL/inc_rp.cl
@@ -651,7 +651,7 @@ DECLSPEC int mangle_replace_nm1 (MAYBE_UNUSED const u8 p0, MAYBE_UNUSED const u8
 
 DECLSPEC int mangle_dupeblock_first (MAYBE_UNUSED const u8 p0, MAYBE_UNUSED const u8 p1, u8 *buf, const int len)
 {
-  if (p0 >= len) return (len);
+  if (p0 > len) return (len);
 
   const int out_len = len + p0;
 
@@ -669,7 +669,7 @@ DECLSPEC int mangle_dupeblock_first (MAYBE_UNUSED const u8 p0, MAYBE_UNUSED cons
 
 DECLSPEC int mangle_dupeblock_last (MAYBE_UNUSED const u8 p0, MAYBE_UNUSED const u8 p1, u8 *buf, const int len)
 {
-  if (p0 >= len) return (len);
+  if (p0 > len) return (len);
 
   const int out_len = len + p0;