diff --git a/crypto/secp256k1/libsecp256k1/contrib/lax_der_parsing.c b/crypto/secp256k1/libsecp256k1/contrib/lax_der_parsing.c
index bf562303ed..484259c3d6 100644
--- a/crypto/secp256k1/libsecp256k1/contrib/lax_der_parsing.c
+++ b/crypto/secp256k1/libsecp256k1/contrib/lax_der_parsing.c
@@ -120,7 +120,7 @@ int ecdsa_signature_parse_der_lax(const secp256k1_context* ctx, secp256k1_ecdsa_
     /* Copy R value */
     if (rlen > 32) {
         overflow = 1;
-    } else if (rlen) {
+    } else if (rlen > 0 && rlen <= 32) {
         memcpy(tmpsig + 32 - rlen, input + rpos, rlen);
     }
 
@@ -132,7 +132,7 @@ int ecdsa_signature_parse_der_lax(const secp256k1_context* ctx, secp256k1_ecdsa_
     /* Copy S value */
     if (slen > 32) {
         overflow = 1;
-    } else if (slen) {
+    } else if (slen > 0 && slen <= 32) {
         memcpy(tmpsig + 64 - slen, input + spos, slen);
     }