diff --git a/builder.go b/builder.go
index f4f4801..3814fa2 100644
--- a/builder.go
+++ b/builder.go
@@ -140,13 +140,34 @@ type Dependency struct {
 	Version string `json:"version,omitempty"`
 }
 
+// ReplacementPath represents an old or new path component
+// within a Go module replacement directive.
+type ReplacementPath string
+
+// Param reformats a go.mod replace directive to be
+// compatible with the `go mod edit` command.
+func (r ReplacementPath) Param() string {
+	return strings.Replace(string(r), " ", "@", 1)
+}
+
+func (r ReplacementPath) String() string { return string(r) }
+
 // Replace represents a Go module replacement.
 type Replace struct {
 	// The import path of the module being replaced.
-	Old string `json:"old,omitempty"`
+	Old ReplacementPath `json:"old,omitempty"`
 
 	// The path to the replacement module.
-	New string `json:"new,omitempty"`
+	New ReplacementPath `json:"new,omitempty"`
+}
+
+// NewReplace creates a new instance of Replace provided old and
+// new Go module paths
+func NewReplace(old, new string) Replace {
+	return Replace{
+		Old: ReplacementPath(old),
+		New: ReplacementPath(new),
+	}
 }
 
 // newTempFolder creates a new folder in a temporary location.
diff --git a/builder_test.go b/builder_test.go
new file mode 100644
index 0000000..a8308f4
--- /dev/null
+++ b/builder_test.go
@@ -0,0 +1,88 @@
+// Copyright 2020 Matthew Holt
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package xcaddy
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+)
+
+func TestReplacementPath_Param(t *testing.T) {
+	tests := []struct {
+		name string
+		r    ReplacementPath
+		want string
+	}{
+		{
+			"Empty",
+			ReplacementPath(""),
+			"",
+		},
+		{
+			"ModulePath",
+			ReplacementPath("github.com/x/y"),
+			"github.com/x/y",
+		},
+		{
+			"ModulePath Version Pinned",
+			ReplacementPath("github.com/x/y v0.0.0-20200101000000-xxxxxxxxxxxx"),
+			"github.com/x/y@v0.0.0-20200101000000-xxxxxxxxxxxx",
+		},
+		{
+			"FilePath",
+			ReplacementPath("/x/y/z"),
+			"/x/y/z",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			fmt.Println(tt.r.Param())
+			if got := tt.r.Param(); got != tt.want {
+				t.Errorf("ReplacementPath.Param() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestNewReplace(t *testing.T) {
+	type args struct {
+		old string
+		new string
+	}
+	tests := []struct {
+		name string
+		args args
+		want Replace
+	}{
+		{
+			"Empty",
+			args{"", ""},
+			Replace{"", ""},
+		},
+		{
+			"Constructor",
+			args{"a", "b"},
+			Replace{"a", "b"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := NewReplace(tt.args.old, tt.args.new); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("NewReplace() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
diff --git a/cmd/xcaddy/main.go b/cmd/xcaddy/main.go
index 950a3d5..50def87 100644
--- a/cmd/xcaddy/main.go
+++ b/cmd/xcaddy/main.go
@@ -74,10 +74,7 @@ func runBuild(ctx context.Context, args []string) error {
 				Version:     ver,
 			})
 			if repl != "" {
-				replacements = append(replacements, xcaddy.Replace{
-					Old: mod,
-					New: repl,
-				})
+				replacements = append(replacements, xcaddy.NewReplace(mod, repl))
 			}
 
 		case "--output":
@@ -168,10 +165,7 @@ func runDev(ctx context.Context, args []string) error {
 	// make sure the module being developed is replaced
 	// so that the local copy is used
 	replacements := []xcaddy.Replace{
-		{
-			Old: currentModule,
-			New: moduleDir,
-		},
+		xcaddy.NewReplace(currentModule, moduleDir),
 	}
 
 	// replace directives only apply to the top-level/main go.mod,
@@ -189,10 +183,10 @@ func runDev(ctx context.Context, args []string) error {
 		if len(parts) != 2 || parts[0] == "" || parts[1] == "" {
 			continue
 		}
-		replacements = append(replacements, xcaddy.Replace{
-			Old: strings.TrimSpace(parts[0]),
-			New: strings.TrimSpace(parts[1]),
-		})
+		replacements = append(replacements, xcaddy.NewReplace(
+			strings.TrimSpace(parts[0]),
+			strings.TrimSpace(parts[1]),
+		))
 	}
 
 	// reconcile remaining path segments; for example if a module foo/a
diff --git a/environment.go b/environment.go
index c00d33f..7b5f6c8 100644
--- a/environment.go
+++ b/environment.go
@@ -109,14 +109,14 @@ func (b Builder) newEnvironment(ctx context.Context) (*environment, error) {
 	// specify module replacements before pinning versions
 	replaced := make(map[string]string)
 	for _, r := range b.Replacements {
-		log.Printf("[INFO] Replace %s => %s", r.Old, r.New)
+		log.Printf("[INFO] Replace %s => %s", r.Old.String(), r.New.String())
 		cmd := env.newCommand("go", "mod", "edit",
-			"-replace", fmt.Sprintf("%s=%s", r.Old, r.New))
+			"-replace", fmt.Sprintf("%s=%s", r.Old.Param(), r.New.Param()))
 		err := env.runCommand(ctx, cmd, 10*time.Second)
 		if err != nil {
 			return nil, err
 		}
-		replaced[r.Old] = r.New
+		replaced[r.Old.String()] = r.New.String()
 	}
 
 	// check for early abort