diff --git a/reflect/protoregistry/registry.go b/reflect/protoregistry/registry.go
index 66dcbcd..3c7ec70 100644
--- a/reflect/protoregistry/registry.go
+++ b/reflect/protoregistry/registry.go
@@ -94,7 +94,8 @@
 	// Note that enum values are in the top-level since that are in the same
 	// scope as the parent enum.
 	descsByName map[protoreflect.FullName]interface{}
-	filesByPath map[string]protoreflect.FileDescriptor
+	filesByPath map[string][]protoreflect.FileDescriptor
+	numFiles    int
 }
 
 type packageDescriptor struct {
@@ -117,17 +118,11 @@
 		r.descsByName = map[protoreflect.FullName]interface{}{
 			"": &packageDescriptor{},
 		}
-		r.filesByPath = make(map[string]protoreflect.FileDescriptor)
+		r.filesByPath = make(map[string][]protoreflect.FileDescriptor)
 	}
 	path := file.Path()
-	if prev := r.filesByPath[path]; prev != nil {
+	if len(r.filesByPath[path]) > 0 {
 		r.checkGenProtoConflict(path)
-		err := errors.New("file %q is already registered", file.Path())
-		err = amendErrorWithCaller(err, prev, file)
-		if r == GlobalFiles && ignoreConflict(file, err) {
-			err = nil
-		}
-		return err
 	}
 
 	for name := file.Package(); name != ""; name = name.Parent() {
@@ -168,7 +163,8 @@
 	rangeTopLevelDescriptors(file, func(d protoreflect.Descriptor) {
 		r.descsByName[d.FullName()] = d
 	})
-	r.filesByPath[path] = file
+	r.filesByPath[path] = append(r.filesByPath[path], file)
+	r.numFiles++
 	return nil
 }
 
@@ -308,6 +304,7 @@
 // FindFileByPath looks up a file by the path.
 //
 // This returns (nil, NotFound) if not found.
+// This returns an error if multiple files have the same path.
 func (r *Files) FindFileByPath(path string) (protoreflect.FileDescriptor, error) {
 	if r == nil {
 		return nil, NotFound
@@ -316,13 +313,19 @@
 		globalMutex.RLock()
 		defer globalMutex.RUnlock()
 	}
-	if fd, ok := r.filesByPath[path]; ok {
-		return fd, nil
+	fds := r.filesByPath[path]
+	switch len(fds) {
+	case 0:
+		return nil, NotFound
+	case 1:
+		return fds[0], nil
+	default:
+		return nil, errors.New("multiple files named %q", path)
 	}
-	return nil, NotFound
 }
 
-// NumFiles reports the number of registered files.
+// NumFiles reports the number of registered files,
+// including duplicate files with the same name.
 func (r *Files) NumFiles() int {
 	if r == nil {
 		return 0
@@ -331,10 +334,11 @@
 		globalMutex.RLock()
 		defer globalMutex.RUnlock()
 	}
-	return len(r.filesByPath)
+	return r.numFiles
 }
 
 // RangeFiles iterates over all registered files while f returns true.
+// If multiple files have the same name, RangeFiles iterates over all of them.
 // The iteration order is undefined.
 func (r *Files) RangeFiles(f func(protoreflect.FileDescriptor) bool) {
 	if r == nil {
@@ -344,9 +348,11 @@
 		globalMutex.RLock()
 		defer globalMutex.RUnlock()
 	}
-	for _, file := range r.filesByPath {
-		if !f(file) {
-			return
+	for _, files := range r.filesByPath {
+		for _, file := range files {
+			if !f(file) {
+				return
+			}
 		}
 	}
 }
diff --git a/reflect/protoregistry/registry_test.go b/reflect/protoregistry/registry_test.go
index 446e036..bc8019c 100644
--- a/reflect/protoregistry/registry_test.go
+++ b/reflect/protoregistry/registry_test.go
@@ -55,6 +55,7 @@
 		testFindPath struct {
 			inPath    string
 			wantFiles []file
+			wantErr   string
 		}
 	)
 
@@ -68,7 +69,7 @@
 		files: []testFile{
 			{inFile: mustMakeFile(`syntax:"proto2" name:"test1.proto" package:"foo.bar"`)},
 			{inFile: mustMakeFile(`syntax:"proto2" name:"foo/bar/test.proto" package:"my.test"`)},
-			{inFile: mustMakeFile(`syntax:"proto2" name:"foo/bar/test.proto" package:"foo.bar.baz"`), wantErr: "already registered"},
+			{inFile: mustMakeFile(`syntax:"proto2" name:"foo/bar/test.proto" package:"foo.bar.baz"`)},
 			{inFile: mustMakeFile(`syntax:"proto2" name:"test2.proto" package:"my.test.package"`)},
 			{inFile: mustMakeFile(`syntax:"proto2" name:"weird" package:"foo.bar"`)},
 			{inFile: mustMakeFile(`syntax:"proto2" name:"foo/bar/baz/../test.proto" package:"my.test"`)},
@@ -103,17 +104,16 @@
 		}},
 
 		findPaths: []testFindPath{{
-			inPath: "nothing",
+			inPath:  "nothing",
+			wantErr: "not found",
 		}, {
 			inPath: "weird",
 			wantFiles: []file{
 				{"weird", "foo.bar"},
 			},
 		}, {
-			inPath: "foo/bar/test.proto",
-			wantFiles: []file{
-				{"foo/bar/test.proto", "my.test"},
-			},
+			inPath:  "foo/bar/test.proto",
+			wantErr: `multiple files named "foo/bar/test.proto"`,
 		}},
 	}, {
 		// Test when new enum conflicts with existing package.
@@ -315,9 +315,13 @@
 
 			for _, tc := range tt.findPaths {
 				var gotFiles []file
-				if fd, err := files.FindFileByPath(tc.inPath); err == nil {
+				fd, gotErr := files.FindFileByPath(tc.inPath)
+				if gotErr == nil {
 					gotFiles = append(gotFiles, file{fd.Path(), fd.Package()})
 				}
+				if ((gotErr == nil) != (tc.wantErr == "")) || !strings.Contains(fmt.Sprint(gotErr), tc.wantErr) {
+					t.Errorf("FindFileByPath(%v) = %v, want %v", tc.inPath, gotErr, tc.wantErr)
+				}
 				if diff := cmp.Diff(tc.wantFiles, gotFiles, sortFiles); diff != "" {
 					t.Errorf("FindFileByPath(%v) mismatch (-want +got):\n%v", tc.inPath, diff)
 				}