diff --git a/reflect/protodesc/protodesc.go b/reflect/protodesc/protodesc.go
index 2ee40ca..4135ade 100644
--- a/reflect/protodesc/protodesc.go
+++ b/reflect/protodesc/protodesc.go
@@ -73,19 +73,12 @@
 		f.Imports[i].IsWeak = true
 	}
 	for i, path := range fd.GetDependency() {
-		var n int
 		imp := &f.Imports[i]
-		r.RangeFilesByPath(path, func(fd protoreflect.FileDescriptor) bool {
-			imp.FileDescriptor = fd
-			n++
-			return true
-		})
-		if n > 1 {
-			return nil, errors.New("duplicate files for import %q", path)
+		fd, err := r.FindFileByPath(path)
+		if err != nil {
+			fd = prototype.PlaceholderFile(path, "")
 		}
-		if imp.IsWeak || imp.FileDescriptor == nil {
-			imp.FileDescriptor = prototype.PlaceholderFile(path, "")
-		}
+		imp.FileDescriptor = fd
 	}
 
 	imps := importedFiles(f.Imports)
diff --git a/reflect/protoregistry/registry.go b/reflect/protoregistry/registry.go
index b778cd2..61b7ac5 100644
--- a/reflect/protoregistry/registry.go
+++ b/reflect/protoregistry/registry.go
@@ -53,7 +53,7 @@
 	// Note that files are stored as a slice, since a package may contain
 	// multiple files.
 	descs       map[protoreflect.FullName]interface{}
-	filesByPath map[string][]protoreflect.FileDescriptor
+	filesByPath map[string]protoreflect.FileDescriptor
 }
 
 type packageDescriptor struct {
@@ -88,7 +88,7 @@
 		r.descs = map[protoreflect.FullName]interface{}{
 			"": &packageDescriptor{},
 		}
-		r.filesByPath = make(map[string][]protoreflect.FileDescriptor)
+		r.filesByPath = make(map[string]protoreflect.FileDescriptor)
 	}
 	var firstErr error
 	for _, file := range files {
@@ -99,6 +99,11 @@
 	return firstErr
 }
 func (r *Files) registerFile(file protoreflect.FileDescriptor) error {
+	path := file.Path()
+	if r.filesByPath[path] != nil {
+		return errors.New("file %q is already registered", file.Path())
+	}
+
 	for name := file.Package(); name != ""; name = name.Parent() {
 		switch r.descs[name].(type) {
 		case nil, *packageDescriptor:
@@ -116,9 +121,6 @@
 		return err
 	}
 
-	path := file.Path()
-	r.filesByPath[path] = append(r.filesByPath[path], file)
-
 	for name := file.Package(); name != ""; name = name.Parent() {
 		if r.descs[name] == nil {
 			r.descs[name] = &packageDescriptor{}
@@ -129,6 +131,7 @@
 	rangeRegisteredDescriptors(file, func(desc protoreflect.Descriptor) {
 		r.descs[desc.FullName()] = desc
 	})
+	r.filesByPath[path] = file
 	return nil
 }
 
@@ -187,6 +190,19 @@
 	return nil, NotFound
 }
 
+// FindFileByPath looks up a file by the path.
+//
+// This returns (nil, NotFound) if not found.
+func (r *Files) FindFileByPath(path string) (protoreflect.FileDescriptor, error) {
+	if r == nil {
+		return nil, NotFound
+	}
+	if fd, ok := r.filesByPath[path]; ok {
+		return fd, nil
+	}
+	return nil, NotFound
+}
+
 // RangeFiles iterates over all registered files.
 // The iteration order is undefined.
 func (r *Files) RangeFiles(f func(protoreflect.FileDescriptor) bool) {
@@ -206,14 +222,14 @@
 
 // RangeFilesByPath iterates over all registered files filtered by
 // the given proto path. The iteration order is undefined.
+//
+// Deprecated: Use FindFileByPath instead.
 func (r *Files) RangeFilesByPath(path string, f func(protoreflect.FileDescriptor) bool) {
 	if r == nil {
 		return
 	}
-	for _, file := range r.filesByPath[path] {
-		if !f(file) {
-			return
-		}
+	if fd, ok := r.filesByPath[path]; ok {
+		f(fd)
 	}
 }
 
diff --git a/reflect/protoregistry/registry_test.go b/reflect/protoregistry/registry_test.go
index 055879a..de0c4a6 100644
--- a/reflect/protoregistry/registry_test.go
+++ b/reflect/protoregistry/registry_test.go
@@ -35,23 +35,23 @@
 			inPkg     pref.FullName
 			wantFiles []file
 		}
-		testRangePath struct {
+		testFindPath struct {
 			inPath    string
 			wantFiles []file
 		}
 	)
 
 	tests := []struct {
-		files      []testFile
-		rangePkgs  []testRangePkg
-		rangePaths []testRangePath
+		files     []testFile
+		rangePkgs []testRangePkg
+		findPaths []testFindPath
 	}{{
 		// Test that overlapping packages and files are permitted.
 		files: []testFile{
-			{inFile: &ptype.File{Syntax: pref.Proto2, Package: "foo.bar"}},
+			{inFile: &ptype.File{Syntax: pref.Proto2, Path: "test1.proto", Package: "foo.bar"}},
 			{inFile: &ptype.File{Syntax: pref.Proto2, Path: "foo/bar/test.proto", Package: "my.test"}},
-			{inFile: &ptype.File{Syntax: pref.Proto2, Path: "foo/bar/test.proto", Package: "foo.bar.baz"}},
-			{inFile: &ptype.File{Syntax: pref.Proto2, Package: "my.test.package"}},
+			{inFile: &ptype.File{Syntax: pref.Proto2, Path: "foo/bar/test.proto", Package: "foo.bar.baz"}, wantErr: "already registered"},
+			{inFile: &ptype.File{Syntax: pref.Proto2, Path: "test2.proto", Package: "my.test.package"}},
 			{inFile: &ptype.File{Syntax: pref.Proto2, Package: "foo.bar"}},
 			{inFile: &ptype.File{Syntax: pref.Proto2, Path: "foo/bar/baz/../test.proto", Package: "my.test"}},
 		},
@@ -71,31 +71,29 @@
 		}, {
 			inPkg: "foo.bar",
 			wantFiles: []file{
-				{"", "foo.bar"},
+				{"test1.proto", "foo.bar"},
 				{"", "foo.bar"},
 			},
 		}, {
-			inPkg: "foo.bar.baz",
+			inPkg: "my.test",
 			wantFiles: []file{
-				{"foo/bar/test.proto", "foo.bar.baz"},
+				{"foo/bar/baz/../test.proto", "my.test"},
+				{"foo/bar/test.proto", "my.test"},
 			},
 		}, {
 			inPkg: "fo",
 		}},
 
-		rangePaths: []testRangePath{{
+		findPaths: []testFindPath{{
 			inPath: "nothing",
 		}, {
 			inPath: "",
 			wantFiles: []file{
 				{"", "foo.bar"},
-				{"", "foo.bar"},
-				{"", "my.test.package"},
 			},
 		}, {
 			inPath: "foo/bar/test.proto",
 			wantFiles: []file{
-				{"foo/bar/test.proto", "foo.bar.baz"},
 				{"foo/bar/test.proto", "my.test"},
 			},
 		}},
@@ -127,6 +125,7 @@
 		files: []testFile{{
 			inFile: &ptype.File{
 				Syntax:  pref.Proto2,
+				Path:    "test1.proto",
 				Package: "fizz.buzz",
 				Messages: []ptype.Message{{
 					Name: "Message",
@@ -165,6 +164,7 @@
 		}, {
 			inFile: &ptype.File{
 				Syntax:  pref.Proto2,
+				Path:    "test2.proto",
 				Package: "fizz.buzz.gazz",
 				Enums: []ptype.Enum{{
 					Name:   "Enum",
@@ -172,9 +172,9 @@
 				}},
 			},
 		}, {
-			// Previously failed registration should not pollute the namespace.
 			inFile: &ptype.File{
 				Syntax:  pref.Proto2,
+				Path:    "test3.proto",
 				Package: "fizz.buzz",
 				Enums: []ptype.Enum{{
 					Name:   "Enum1",
@@ -213,7 +213,7 @@
 					t.Fatalf("file %d, prototype.NewFile() error: %v", i, err)
 				}
 				gotErr := files.Register(fd)
-				if (gotErr == nil && tc.wantErr != "") || !strings.Contains(fmt.Sprint(gotErr), tc.wantErr) {
+				if ((gotErr == nil) != (tc.wantErr == "")) || !strings.Contains(fmt.Sprint(gotErr), tc.wantErr) {
 					t.Errorf("file %d, Register() = %v, want %v", i, gotErr, tc.wantErr)
 				}
 			}
@@ -229,14 +229,13 @@
 				}
 			}
 
-			for _, tc := range tt.rangePaths {
+			for _, tc := range tt.findPaths {
 				var gotFiles []file
-				files.RangeFilesByPath(tc.inPath, func(fd pref.FileDescriptor) bool {
+				if fd, err := files.FindFileByPath(tc.inPath); err == nil {
 					gotFiles = append(gotFiles, file{fd.Path(), fd.Package()})
-					return true
-				})
+				}
 				if diff := cmp.Diff(tc.wantFiles, gotFiles, sortFiles); diff != "" {
-					t.Errorf("RangeFilesByPath(%v) mismatch (-want +got):\n%v", tc.inPath, diff)
+					t.Errorf("FindFileByPath(%v) mismatch (-want +got):\n%v", tc.inPath, diff)
 				}
 			}
 		})