diff --git a/cmd/api-router.go b/cmd/api-router.go
index 3b7751888..76a3ddc28 100644
--- a/cmd/api-router.go
+++ b/cmd/api-router.go
@@ -245,10 +245,10 @@ func registerAPIRouter(router *mux.Router) {
 		router.Methods(http.MethodPut).Path("/{object:.+}").
 			HeadersRegexp(xhttp.AmzCopySource, ".*?(\\/|%2F).*?").
 			HandlerFunc(collectAPIStats("copyobjectpart", maxClients(gz(httpTraceAll(api.CopyObjectPartHandler))))).
-			Queries("partNumber", "{partNumber:[0-9]+}", "uploadId", "{uploadId:.*}")
+			Queries("partNumber", "{partNumber:.*}", "uploadId", "{uploadId:.*}")
 		// PutObjectPart
 		router.Methods(http.MethodPut).Path("/{object:.+}").HandlerFunc(
-			collectAPIStats("putobjectpart", maxClients(gz(httpTraceHdrs(api.PutObjectPartHandler))))).Queries("partNumber", "{partNumber:[0-9]+}", "uploadId", "{uploadId:.*}")
+			collectAPIStats("putobjectpart", maxClients(gz(httpTraceHdrs(api.PutObjectPartHandler))))).Queries("partNumber", "{partNumber:.*}", "uploadId", "{uploadId:.*}")
 		// ListObjectParts
 		router.Methods(http.MethodGet).Path("/{object:.+}").HandlerFunc(
 			collectAPIStats("listobjectparts", maxClients(gz(httpTraceAll(api.ListObjectPartsHandler))))).Queries("uploadId", "{uploadId:.*}")
diff --git a/cmd/object-handlers_test.go b/cmd/object-handlers_test.go
index 97ce3574c..e603e4c25 100644
--- a/cmd/object-handlers_test.go
+++ b/cmd/object-handlers_test.go
@@ -3693,6 +3693,27 @@ func testAPIPutObjectPartHandler(obj ObjectLayer, instanceType, bucketName strin
 
 			expectedAPIError: ErrInvalidAccessKeyID,
 		},
+		// Case where part number is invalid.
+		9: {
+			objectName: testObject,
+			content:    "hello",
+			partNumber: "0",
+			fault:      None,
+			accessKey:  credentials.AccessKey,
+			secretKey:  credentials.SecretKey,
+
+			expectedAPIError: ErrInvalidPart,
+		},
+		10: {
+			objectName: testObject,
+			content:    "hello",
+			partNumber: "-10",
+			fault:      None,
+			accessKey:  credentials.AccessKey,
+			secretKey:  credentials.SecretKey,
+
+			expectedAPIError: ErrInvalidPart,
+		},
 	}
 
 	reqV2Str := "V2 Signed HTTP request"
diff --git a/cmd/object-multipart-handlers.go b/cmd/object-multipart-handlers.go
index 6cf110cb1..7f9e366ab 100644
--- a/cmd/object-multipart-handlers.go
+++ b/cmd/object-multipart-handlers.go
@@ -285,7 +285,7 @@ func (api objectAPIHandlers) CopyObjectPartHandler(w http.ResponseWriter, r *htt
 	partIDString := r.Form.Get(xhttp.PartNumber)
 
 	partID, err := strconv.Atoi(partIDString)
-	if err != nil {
+	if err != nil || partID <= 0 {
 		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrInvalidPart), r.URL)
 		return
 	}
@@ -615,7 +615,7 @@ func (api objectAPIHandlers) PutObjectPartHandler(w http.ResponseWriter, r *http
 	partIDString := r.Form.Get(xhttp.PartNumber)
 
 	partID, err := strconv.Atoi(partIDString)
-	if err != nil {
+	if err != nil || partID <= 0 {
 		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrInvalidPart), r.URL)
 		return
 	}
diff --git a/cmd/test-utils_test.go b/cmd/test-utils_test.go
index c3ba383e8..c08843752 100644
--- a/cmd/test-utils_test.go
+++ b/cmd/test-utils_test.go
@@ -2008,10 +2008,10 @@ func registerBucketLevelFunc(bucket *mux.Router, api objectAPIHandlers, apiFunct
 			bucket.Methods(http.MethodPost).Path("/{object:.+}").HandlerFunc(api.NewMultipartUploadHandler).Queries("uploads", "")
 		case "CopyObjectPart":
 			// Register CopyObjectPart handler.
-			bucket.Methods(http.MethodPut).Path("/{object:.+}").HeadersRegexp("X-Amz-Copy-Source", ".*?(\\/|%2F).*?").HandlerFunc(api.CopyObjectPartHandler).Queries("partNumber", "{partNumber:[0-9]+}", "uploadId", "{uploadId:.*}")
+			bucket.Methods(http.MethodPut).Path("/{object:.+}").HeadersRegexp("X-Amz-Copy-Source", ".*?(\\/|%2F).*?").HandlerFunc(api.CopyObjectPartHandler).Queries("partNumber", "{partNumber:.*}", "uploadId", "{uploadId:.*}")
 		case "PutObjectPart":
 			// Register PutObjectPart handler.
-			bucket.Methods(http.MethodPut).Path("/{object:.+}").HandlerFunc(api.PutObjectPartHandler).Queries("partNumber", "{partNumber:[0-9]+}", "uploadId", "{uploadId:.*}")
+			bucket.Methods(http.MethodPut).Path("/{object:.+}").HandlerFunc(api.PutObjectPartHandler).Queries("partNumber", "{partNumber:.*}", "uploadId", "{uploadId:.*}")
 		case "ListObjectParts":
 			// Register ListObjectParts handler.
 			bucket.Methods(http.MethodGet).Path("/{object:.+}").HandlerFunc(api.ListObjectPartsHandler).Queries("uploadId", "{uploadId:.*}")