diff --git a/cmd/prdescribe.go b/cmd/prdescribe.go
index 7398ada..edc5415 100644
--- a/cmd/prdescribe.go
+++ b/cmd/prdescribe.go
@@ -2,12 +2,17 @@ package cmd
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/fatih/color"
 	"github.com/spf13/cobra"
 	"gmgauthier.com/grokkit/config"
+	"gmgauthier.com/grokkit/internal/git"
 )
 
+// gitDiff is the mockable entry point (exactly like gitRun used elsewhere).
+var gitDiff = git.Diff
+
 var prDescribeCmd = &cobra.Command{
 	Use:   "pr-describe",
 	Short: "Generate full PR description from current branch",
@@ -15,30 +20,32 @@ var prDescribeCmd = &cobra.Command{
 }
 
 func init() {
-	prDescribeCmd.Flags().StringP("base", "b", "master", "Base branch to compare against")
+	prDescribeCmd.Flags().StringP("base", "b", "master", "Base branch to compare against (default: master)")
 }
 
 func runPRDescribe(cmd *cobra.Command, _ []string) {
 	base, _ := cmd.Flags().GetString("base")
 
-	diff, err := gitRun([]string{"diff", fmt.Sprintf("%s..HEAD", base), "--no-color"})
-	if err != nil || diff == "" {
-		diff, err = gitRun([]string{"diff", fmt.Sprintf("origin/%s..HEAD", base), "--no-color"})
+	// Prefer local base, fallback to origin/<base>.
+	diff, err := gitDiff([]string{"diff", fmt.Sprintf("%s..HEAD", base), "--no-color"})
+	if err != nil || strings.TrimSpace(diff) == "" {
+		diff, err = gitDiff([]string{"diff", fmt.Sprintf("origin/%s..HEAD", base), "--no-color"})
 		if err != nil {
 			color.Red("Failed to get branch diff: %v", err)
 			return
 		}
 	}
-	if diff == "" {
+	if strings.TrimSpace(diff) == "" {
 		color.Yellow("No changes on this branch compared to %s/origin/%s.", base, base)
 		return
 	}
+
 	modelFlag, _ := cmd.Flags().GetString("model")
 	model := config.GetModel("prdescribe", modelFlag)
 
 	client := newGrokClient()
 	messages := buildPRDescribeMessages(diff)
-	color.Yellow("Writing PR description...")
+	color.Yellow("Writing PR description (base=%s)...", base)
 	client.Stream(messages, model)
 }
 
diff --git a/cmd/run_test.go b/cmd/run_test.go
index 859f40d..bed9c2a 100644
--- a/cmd/run_test.go
+++ b/cmd/run_test.go
@@ -47,6 +47,13 @@ func withMockGit(fn func([]string) (string, error)) func() {
 	return func() { gitRun = orig }
 }
 
+// withMockGitDiff injects a fake for the new git.Diff (mockable var).
+func withMockGitDiff(fn func([]string) (string, error)) func() {
+	orig := gitDiff
+	gitDiff = fn
+	return func() { gitDiff = orig }
+}
+
 // testCmd returns a minimal cobra command with common flags registered.
 func testCmd() *cobra.Command {
 	c := &cobra.Command{}
@@ -260,7 +267,7 @@ func TestRunPRDescribe(t *testing.T) {
 	t.Run("no changes on branch — skips AI", func(t *testing.T) {
 		mock := &mockStreamer{}
 		defer withMockClient(mock)()
-		defer withMockGit(func(args []string) (string, error) {
+		defer withMockGitDiff(func(args []string) (string, error) {
 			return "", nil // both diff calls return empty
 		})()
 
@@ -275,7 +282,7 @@ func TestRunPRDescribe(t *testing.T) {
 		mock := &mockStreamer{response: "## PR Title\n\nDescription"}
 		defer withMockClient(mock)()
 		callCount := 0
-		defer withMockGit(func(args []string) (string, error) {
+		defer withMockGitDiff(func(args []string) (string, error) {
 			callCount++
 			if callCount == 1 {
 				return "diff --git a/foo.go b/foo.go", nil
@@ -294,7 +301,7 @@ func TestRunPRDescribe(t *testing.T) {
 		mock := &mockStreamer{response: "PR description"}
 		defer withMockClient(mock)()
 		callCount := 0
-		defer withMockGit(func(args []string) (string, error) {
+		defer withMockGitDiff(func(args []string) (string, error) {
 			callCount++
 			if callCount == 2 {
 				return "diff --git a/bar.go b/bar.go", nil
@@ -313,7 +320,7 @@ func TestRunPRDescribe(t *testing.T) {
 		mock := &mockStreamer{response: "PR description"}
 		defer withMockClient(mock)()
 		var capturedArgs []string
-		defer withMockGit(func(args []string) (string, error) {
+		defer withMockGitDiff(func(args []string) (string, error) {
 			capturedArgs = args
 			return "diff content", nil
 		})()
@@ -345,7 +352,7 @@ func TestRunPRDescribe(t *testing.T) {
 		mock := &mockStreamer{response: "PR description"}
 		defer withMockClient(mock)()
 		var capturedArgs []string
-		defer withMockGit(func(args []string) (string, error) {
+		defer withMockGitDiff(func(args []string) (string, error) {
 			capturedArgs = args
 			return "diff content", nil
 		})()
diff --git a/internal/git/git.go b/internal/git/git.go
index 48556ad..b6db72b 100644
--- a/internal/git/git.go
+++ b/internal/git/git.go
@@ -1,6 +1,7 @@
 package git
 
 import (
+	"errors"
 	"fmt"
 	"os/exec"
 	"strings"
@@ -60,3 +61,24 @@ func LogSince(since string) (string, error) {
 	args := []string{"log", "--pretty=format:%s%n%b%n---", since + "..HEAD"}
 	return Run(args)
 }
+
+// Diff runs `git diff` and tolerates exit code 1 (differences found).
+// This is normal git behavior when there *are* changes — unlike .Output().
+func Diff(args []string) (string, error) {
+	cmdStr := "git " + strings.Join(args, " ")
+	logger.Debug("executing git diff", "command", cmdStr)
+
+	// nolint:gosec // intentional git subprocess
+	cmd := exec.Command("git", args...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		var exitErr *exec.ExitError
+		if errors.As(err, &exitErr) && exitErr.ExitCode() == 1 {
+			// legitimate diff (changes exist)
+			return string(out), nil
+		}
+		logger.Error("git diff failed", "command", cmdStr, "error", err)
+		return "", fmt.Errorf("git diff failed: %w", err)
+	}
+	return string(out), nil
+}