diff --git a/Modules/_pickle.c b/Modules/_pickle.c
index c6cb8bc..830479f 100644
--- a/Modules/_pickle.c
+++ b/Modules/_pickle.c
@@ -4540,7 +4540,17 @@
     int i;
     size_t x = 0;
 
-    for (i = 0; i < nbytes && i < sizeof(size_t); i++) {
+    if (nbytes > (int)sizeof(size_t)) {
+        /* Check for integer overflow.  BINBYTES8 and BINUNICODE8 opcodes
+         * have 64-bit size that can't be represented on 32-bit platform.
+         */
+        for (i = (int)sizeof(size_t); i < nbytes; i++) {
+            if (s[i])
+                return -1;
+        }
+        nbytes = (int)sizeof(size_t);
+    }
+    for (i = 0; i < nbytes; i++) {
         x |= (size_t) s[i] << (8 * i);
     }