diff --git a/src/config/schema.ts b/src/config/schema.ts
index 0d2c590ba..bcb36a175 100644
--- a/src/config/schema.ts
+++ b/src/config/schema.ts
@@ -10,6 +10,7 @@ export * from "./schema/commands"
 export * from "./schema/dynamic-context-pruning"
 export * from "./schema/experimental"
 export * from "./schema/fallback-models"
+export * from "./schema/git-env-prefix"
 export * from "./schema/git-master"
 export * from "./schema/hooks"
 export * from "./schema/notification"
diff --git a/src/config/schema/git-env-prefix.ts b/src/config/schema/git-env-prefix.ts
new file mode 100644
index 000000000..65609c0b1
--- /dev/null
+++ b/src/config/schema/git-env-prefix.ts
@@ -0,0 +1,28 @@
+import { z } from "zod"
+
+const GIT_ENV_ASSIGNMENT_PATTERN =
+	/^(?:[A-Za-z_][A-Za-z0-9_]*=[A-Za-z0-9_-]*)(?: [A-Za-z_][A-Za-z0-9_]*=[A-Za-z0-9_-]*)*$/
+
+export const GIT_ENV_PREFIX_VALIDATION_MESSAGE =
+	'git_env_prefix must be empty or use shell-safe env assignments like "GIT_MASTER=1"'
+
+export function isValidGitEnvPrefix(value: string): boolean {
+	if (value === "") {
+		return true
+	}
+
+	return GIT_ENV_ASSIGNMENT_PATTERN.test(value)
+}
+
+export function assertValidGitEnvPrefix(value: string): string {
+	if (!isValidGitEnvPrefix(value)) {
+		throw new Error(GIT_ENV_PREFIX_VALIDATION_MESSAGE)
+	}
+
+	return value
+}
+
+export const GitEnvPrefixSchema = z
+	.string()
+	.refine(isValidGitEnvPrefix, { message: GIT_ENV_PREFIX_VALIDATION_MESSAGE })
+	.default("GIT_MASTER=1")
diff --git a/src/config/schema/git-master.ts b/src/config/schema/git-master.ts
index e162b38c5..4c6f4bf65 100644
--- a/src/config/schema/git-master.ts
+++ b/src/config/schema/git-master.ts
@@ -1,12 +1,14 @@
 import { z } from "zod"
 
+import { GitEnvPrefixSchema } from "./git-env-prefix"
+
 export const GitMasterConfigSchema = z.object({
   /** Add "Ultraworked with Sisyphus" footer to commit messages (default: true). Can be boolean or custom string. */
   commit_footer: z.union([z.boolean(), z.string()]).default(true),
   /** Add "Co-authored-by: Sisyphus" trailer to commit messages (default: true) */
   include_co_authored_by: z.boolean().default(true),
   /** Environment variable prefix for all git commands (default: "GIT_MASTER=1"). Set to "" to disable. Allows custom git hooks to detect git-master skill usage. */
-  git_env_prefix: z.string().default("GIT_MASTER=1"),
+  git_env_prefix: GitEnvPrefixSchema,
 })
 
 export type GitMasterConfig = z.infer<typeof GitMasterConfigSchema>