diff --git a/src/hooks/non-interactive-env/index.test.ts b/src/hooks/non-interactive-env/index.test.ts
index 7eed35294..8e4bed295 100644
--- a/src/hooks/non-interactive-env/index.test.ts
+++ b/src/hooks/non-interactive-env/index.test.ts
@@ -111,6 +111,34 @@ describe("non-interactive-env hook", () => {
 
       expect(output.args.command).toBeUndefined()
     })
+
+    test("#given git command already has prefix #when hook executes again #then does not duplicate prefix", async () => {
+      const hook = createNonInteractiveEnvHook(mockCtx)
+      
+      // First call: transforms the command
+      const output1: { args: Record<string, unknown>; message?: string } = {
+        args: { command: "git commit -m 'test'" },
+      }
+      await hook["tool.execute.before"](
+        { tool: "bash", sessionID: "test", callID: "1" },
+        output1
+      )
+      
+      const firstResult = output1.args.command as string
+      expect(firstResult).toStartWith("export ")
+      
+      // Second call: takes the already-prefixed command
+      const output2: { args: Record<string, unknown>; message?: string } = {
+        args: { command: firstResult },
+      }
+      await hook["tool.execute.before"](
+        { tool: "bash", sessionID: "test", callID: "2" },
+        output2
+      )
+      
+      // Should be exactly the same (no double prefix)
+      expect(output2.args.command).toBe(firstResult)
+    })
   })
 
   describe("shell escaping", () => {
diff --git a/src/hooks/non-interactive-env/non-interactive-env-hook.ts b/src/hooks/non-interactive-env/non-interactive-env-hook.ts
index 90686f64d..758a1eb78 100644
--- a/src/hooks/non-interactive-env/non-interactive-env-hook.ts
+++ b/src/hooks/non-interactive-env/non-interactive-env-hook.ts
@@ -55,6 +55,13 @@ export function createNonInteractiveEnvHook(_ctx: PluginInput) {
       // The bash tool always runs in a Unix-like shell (bash/sh), even on Windows
       // (via Git Bash, WSL, etc.), so always use unix export syntax.
       const envPrefix = buildEnvPrefix(NON_INTERACTIVE_ENV, "unix")
+      
+      // Check if the command already starts with the prefix to avoid stacking.
+      // This maintains the non-interactive behavior and makes the operation idempotent.
+      if (command.trim().startsWith(envPrefix.trim())) {
+        return
+      }
+
       output.args.command = `${envPrefix} ${command}`
 
       log(`[${HOOK_NAME}] Prepended non-interactive env vars to git command`, {