diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index d8e2d31e..9ad50c1d 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -39,7 +39,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go: ["1.23", "1.24", "1.25.0-rc.3"]
+        go: ["1.23", "1.24", "1.25"]
     steps:
       - name: Check out code
         uses: actions/checkout@v4
diff --git a/mcp/cmd.go b/mcp/cmd.go
index 55e5cca6..b531eaf1 100644
--- a/mcp/cmd.go
+++ b/mcp/cmd.go
@@ -13,9 +13,7 @@ import (
 	"time"
 )
 
-const (
-	defaultTerminateDuration = 5 * time.Second
-)
+var defaultTerminateDuration = 5 * time.Second // mutable for testing
 
 // A CommandTransport is a [Transport] that runs a command and communicates
 // with it over stdin/stdout, using newline-delimited JSON.
diff --git a/mcp/cmd_export_test.go b/mcp/cmd_export_test.go
new file mode 100644
index 00000000..331e8bd0
--- /dev/null
+++ b/mcp/cmd_export_test.go
@@ -0,0 +1,20 @@
+// Copyright 2025 The Go MCP SDK Authors. All rights reserved.
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+package mcp
+
+import "time"
+
+// This file exports some helpers for mutating internals of the command
+// transport for testing.
+
+// SetDefaultTerminateDuration sets the default command terminate duration,
+// and returns a function to reset it to the default.
+func SetDefaultTerminateDuration(d time.Duration) (reset func()) {
+	initial := defaultTerminateDuration
+	defaultTerminateDuration = d
+	return func() {
+		defaultTerminateDuration = initial
+	}
+}
diff --git a/mcp/cmd_test.go b/mcp/cmd_test.go
index 146cbe1f..0df45708 100644
--- a/mcp/cmd_test.go
+++ b/mcp/cmd_test.go
@@ -257,25 +257,35 @@ func TestCommandTransportTerminateDuration(t *testing.T) {
 	}
 	requireExec(t)
 
+	// Unfortunately, since it does I/O, this test needs to rely on timing (we
+	// can't use synctest). However, we can still decreate the default
+	// termination duration to speed up the test.
+	const defaultDur = 50 * time.Millisecond
+	defer mcp.SetDefaultTerminateDuration(defaultDur)()
+
 	tests := []struct {
 		name            string
 		duration        time.Duration
+		wantMinDuration time.Duration
 		wantMaxDuration time.Duration
 	}{
 		{
 			name:            "default duration (zero)",
 			duration:        0,
-			wantMaxDuration: 6 * time.Second, // default 5s + buffer
+			wantMinDuration: defaultDur,
+			wantMaxDuration: 1 * time.Second, // default + buffer
 		},
 		{
 			name:            "below minimum duration",
-			duration:        500 * time.Millisecond,
-			wantMaxDuration: 6 * time.Second, // should use default 5s + buffer
+			duration:        -500 * time.Millisecond,
+			wantMinDuration: defaultDur,
+			wantMaxDuration: 1 * time.Second, // should use default + buffer
 		},
 		{
 			name:            "custom valid duration",
-			duration:        2 * time.Second,
-			wantMaxDuration: 3 * time.Second, // custom 2s + buffer
+			duration:        200 * time.Millisecond,
+			wantMinDuration: 200 * time.Millisecond,
+			wantMaxDuration: 1 * time.Second, // custom + buffer
 		},
 	}
 
@@ -306,7 +316,9 @@ func TestCommandTransportTerminateDuration(t *testing.T) {
 					t.Fatalf("Close() failed with unexpected error: %v", err)
 				}
 			}
-
+			if elapsed < tt.wantMinDuration {
+				t.Errorf("Close() took %v, expected at least %v", elapsed, tt.wantMinDuration)
+			}
 			if elapsed > tt.wantMaxDuration {
 				t.Errorf("Close() took %v, expected at most %v", elapsed, tt.wantMaxDuration)
 			}