diff --git a/lib/common/zstd_internal.h b/lib/common/zstd_internal.h
index a5002fb1..96e05775 100644
--- a/lib/common/zstd_internal.h
+++ b/lib/common/zstd_internal.h
@@ -147,7 +147,7 @@ static void ZSTD_copy8(void* dst, const void* src) { memcpy(dst, src, 8); }
 /*! ZSTD_wildcopy() :
 *   custom version of memcpy(), can copy up to 7 bytes too many (8 bytes if length==0) */
 #define WILDCOPY_OVERLENGTH 8
-MEM_STATIC void ZSTD_wildcopy(void* dst, const void* src, size_t length)
+MEM_STATIC void ZSTD_wildcopy(void* dst, const void* src, ptrdiff_t length)
 {
     const BYTE* ip = (const BYTE*)src;
     BYTE* op = (BYTE*)dst;
diff --git a/lib/decompress/zstd_decompress.c b/lib/decompress/zstd_decompress.c
index 1422d2b3..085477bf 100644
--- a/lib/decompress/zstd_decompress.c
+++ b/lib/decompress/zstd_decompress.c
@@ -997,7 +997,7 @@ size_t ZSTD_execSequence(BYTE* op,
         }
         while (op < oMatchEnd) *op++ = *match++;
     } else {
-        ZSTD_wildcopy(op, match, sequence.matchLength-8);   /* works even if matchLength < 8 */
+        ZSTD_wildcopy(op, match, (ptrdiff_t)sequence.matchLength-8);   /* works even if matchLength < 8 */
     }
     return sequenceLength;
 }
@@ -1218,7 +1218,7 @@ size_t ZSTD_execSequenceLong(BYTE* op,
         }
         while (op < oMatchEnd) *op++ = *match++;
     } else {
-        ZSTD_wildcopy(op, match, sequence.matchLength-8);   /* works even if matchLength < 8 */
+        ZSTD_wildcopy(op, match, (ptrdiff_t)sequence.matchLength-8);   /* works even if matchLength < 8 */
     }
     return sequenceLength;
 }
diff --git a/lib/legacy/zstd_v01.c b/lib/legacy/zstd_v01.c
index 7c8b0f1e..6fd30c0a 100644
--- a/lib/legacy/zstd_v01.c
+++ b/lib/legacy/zstd_v01.c
@@ -1354,7 +1354,7 @@ static void   ZSTD_copy8(void* dst, const void* src) { memcpy(dst, src, 8); }
 
 #define COPY8(d,s)    { ZSTD_copy8(d,s); d+=8; s+=8; }
 
-static void ZSTD_wildcopy(void* dst, const void* src, size_t length)
+static void ZSTD_wildcopy(void* dst, const void* src, ptrdiff_t length)
 {
     const BYTE* ip = (const BYTE*)src;
     BYTE* op = (BYTE*)dst;
@@ -1814,7 +1814,7 @@ static size_t ZSTD_execSequence(BYTE* op,
             while (op<endMatch) *op++ = *match++;
         }
         else
-            ZSTD_wildcopy(op, match, sequence.matchLength-8);   /* works even if matchLength < 8 */
+            ZSTD_wildcopy(op, match, (ptrdiff_t)sequence.matchLength-8);   /* works even if matchLength < 8 */
 
         /* restore, in case of overlap */
         if (overlapRisk) memcpy(endMatch, saved, qutt);
diff --git a/lib/legacy/zstd_v02.c b/lib/legacy/zstd_v02.c
index 135b5bc9..b8a12ab5 100644
--- a/lib/legacy/zstd_v02.c
+++ b/lib/legacy/zstd_v02.c
@@ -2808,7 +2808,7 @@ static void   ZSTD_copy8(void* dst, const void* src) { memcpy(dst, src, 8); }
 #define COPY8(d,s) { ZSTD_copy8(d,s); d+=8; s+=8; }
 
 /*! ZSTD_wildcopy : custom version of memcpy(), can copy up to 7-8 bytes too many */
-static void ZSTD_wildcopy(void* dst, const void* src, size_t length)
+static void ZSTD_wildcopy(void* dst, const void* src, ptrdiff_t length)
 {
     const BYTE* ip = (const BYTE*)src;
     BYTE* op = (BYTE*)dst;
@@ -3218,7 +3218,7 @@ static size_t ZSTD_execSequence(BYTE* op,
         }
         else
         {
-            ZSTD_wildcopy(op, match, sequence.matchLength-8);   /* works even if matchLength < 8 */
+            ZSTD_wildcopy(op, match, (ptrdiff_t)sequence.matchLength-8);   /* works even if matchLength < 8 */
         }
     }
 
diff --git a/lib/legacy/zstd_v03.c b/lib/legacy/zstd_v03.c
index 8cb5928f..6459da3d 100644
--- a/lib/legacy/zstd_v03.c
+++ b/lib/legacy/zstd_v03.c
@@ -2449,7 +2449,7 @@ static void   ZSTD_copy8(void* dst, const void* src) { memcpy(dst, src, 8); }
 #define COPY8(d,s) { ZSTD_copy8(d,s); d+=8; s+=8; }
 
 /*! ZSTD_wildcopy : custom version of memcpy(), can copy up to 7-8 bytes too many */
-static void ZSTD_wildcopy(void* dst, const void* src, size_t length)
+static void ZSTD_wildcopy(void* dst, const void* src, ptrdiff_t length)
 {
     const BYTE* ip = (const BYTE*)src;
     BYTE* op = (BYTE*)dst;
@@ -2859,7 +2859,7 @@ static size_t ZSTD_execSequence(BYTE* op,
         }
         else
         {
-            ZSTD_wildcopy(op, match, sequence.matchLength-8);   /* works even if matchLength < 8 */
+            ZSTD_wildcopy(op, match, (ptrdiff_t)sequence.matchLength-8);   /* works even if matchLength < 8 */
         }
     }
 
diff --git a/lib/legacy/zstd_v04.c b/lib/legacy/zstd_v04.c
index 60cde97c..bd011319 100644
--- a/lib/legacy/zstd_v04.c
+++ b/lib/legacy/zstd_v04.c
@@ -487,7 +487,7 @@ static void ZSTD_copy8(void* dst, const void* src) { memcpy(dst, src, 8); }
 #define COPY8(d,s) { ZSTD_copy8(d,s); d+=8; s+=8; }
 
 /*! ZSTD_wildcopy : custom version of memcpy(), can copy up to 7-8 bytes too many */
-static void ZSTD_wildcopy(void* dst, const void* src, size_t length)
+static void ZSTD_wildcopy(void* dst, const void* src, ptrdiff_t length)
 {
     const BYTE* ip = (const BYTE*)src;
     BYTE* op = (BYTE*)dst;
@@ -3146,7 +3146,7 @@ static size_t ZSTD_execSequence(BYTE* op,
     }
     else
     {
-        ZSTD_wildcopy(op, match, sequence.matchLength-8);   /* works even if matchLength < 8 */
+        ZSTD_wildcopy(op, match, (ptrdiff_t)sequence.matchLength-8);   /* works even if matchLength < 8 */
     }
     return sequenceLength;
 }
diff --git a/lib/legacy/zstd_v05.c b/lib/legacy/zstd_v05.c
index 3dcf7039..3dd740e5 100644
--- a/lib/legacy/zstd_v05.c
+++ b/lib/legacy/zstd_v05.c
@@ -509,7 +509,7 @@ static void ZSTDv05_copy8(void* dst, const void* src) { memcpy(dst, src, 8); }
 
 /*! ZSTDv05_wildcopy() :
 *   custom version of memcpy(), can copy up to 7 bytes too many (8 bytes if length==0) */
-MEM_STATIC void ZSTDv05_wildcopy(void* dst, const void* src, size_t length)
+MEM_STATIC void ZSTDv05_wildcopy(void* dst, const void* src, ptrdiff_t length)
 {
     const BYTE* ip = (const BYTE*)src;
     BYTE* op = (BYTE*)dst;
@@ -3357,7 +3357,7 @@ static size_t ZSTDv05_execSequence(BYTE* op,
         while (op < oMatchEnd)
             *op++ = *match++;
     } else {
-        ZSTDv05_wildcopy(op, match, sequence.matchLength-8);   /* works even if matchLength < 8 */
+        ZSTDv05_wildcopy(op, match, (ptrdiff_t)sequence.matchLength-8);   /* works even if matchLength < 8 */
     }
     return sequenceLength;
 }
diff --git a/lib/legacy/zstd_v06.c b/lib/legacy/zstd_v06.c
index 8aa6dc99..8be4bc37 100644
--- a/lib/legacy/zstd_v06.c
+++ b/lib/legacy/zstd_v06.c
@@ -537,7 +537,7 @@ static void ZSTDv06_copy8(void* dst, const void* src) { memcpy(dst, src, 8); }
 /*! ZSTDv06_wildcopy() :
 *   custom version of memcpy(), can copy up to 7 bytes too many (8 bytes if length==0) */
 #define WILDCOPY_OVERLENGTH 8
-MEM_STATIC void ZSTDv06_wildcopy(void* dst, const void* src, size_t length)
+MEM_STATIC void ZSTDv06_wildcopy(void* dst, const void* src, ptrdiff_t length)
 {
     const BYTE* ip = (const BYTE*)src;
     BYTE* op = (BYTE*)dst;
@@ -3503,7 +3503,7 @@ size_t ZSTDv06_execSequence(BYTE* op,
         }
         while (op < oMatchEnd) *op++ = *match++;
     } else {
-        ZSTDv06_wildcopy(op, match, sequence.matchLength-8);   /* works even if matchLength < 8 */
+        ZSTDv06_wildcopy(op, match, (ptrdiff_t)sequence.matchLength-8);   /* works even if matchLength < 8 */
     }
     return sequenceLength;
 }
diff --git a/lib/legacy/zstd_v07.c b/lib/legacy/zstd_v07.c
index 7719ba08..b607ec37 100644
--- a/lib/legacy/zstd_v07.c
+++ b/lib/legacy/zstd_v07.c
@@ -2845,7 +2845,7 @@ static void ZSTDv07_copy8(void* dst, const void* src) { memcpy(dst, src, 8); }
 /*! ZSTDv07_wildcopy() :
 *   custom version of memcpy(), can copy up to 7 bytes too many (8 bytes if length==0) */
 #define WILDCOPY_OVERLENGTH 8
-MEM_STATIC void ZSTDv07_wildcopy(void* dst, const void* src, size_t length)
+MEM_STATIC void ZSTDv07_wildcopy(void* dst, const void* src, ptrdiff_t length)
 {
     const BYTE* ip = (const BYTE*)src;
     BYTE* op = (BYTE*)dst;
@@ -3726,7 +3726,7 @@ size_t ZSTDv07_execSequence(BYTE* op,
         }
         while (op < oMatchEnd) *op++ = *match++;
     } else {
-        ZSTDv07_wildcopy(op, match, sequence.matchLength-8);   /* works even if matchLength < 8 */
+        ZSTDv07_wildcopy(op, match, (ptrdiff_t)sequence.matchLength-8);   /* works even if matchLength < 8 */
     }
     return sequenceLength;
 }