diff --git a/internal/diff/git.go b/internal/diff/git.go
index 33254f2..765516b 100644
--- a/internal/diff/git.go
+++ b/internal/diff/git.go
@@ -115,14 +115,14 @@ func (p *Provider) GetDiff(ctx context.Context) ([]model.Diff, error) {
 		if base == "" {
 			return nil, fmt.Errorf("cannot find merge-base between %s and %s", p.from, p.to)
 		}
-		out, err := p.runGit(ctx, "diff", "--no-ext-diff", "--no-textconv", "--no-color", "-U"+fmt.Sprint(DiffContextLines), base, p.to, "--")
+		out, err := p.runGit(ctx, "diff", "--no-ext-diff", "--no-textconv", "--src-prefix=a/", "--dst-prefix=b/", "--no-color", "-U"+fmt.Sprint(DiffContextLines), base, p.to, "--")
 		if err != nil {
 			return nil, fmt.Errorf("git diff failed: %w", err)
 		}
 		combined.WriteString(out)
 
 	case ModeCommit:
-		out, err := p.runGit(ctx, "show", "--no-ext-diff", "--no-textconv", "--no-color", "-U"+fmt.Sprint(DiffContextLines), p.commit)
+		out, err := p.runGit(ctx, "show", "--no-ext-diff", "--no-textconv", "--src-prefix=a/", "--dst-prefix=b/", "--no-color", "-U"+fmt.Sprint(DiffContextLines), p.commit)
 		if err != nil {
 			return nil, fmt.Errorf("git show failed: %w", err)
 		}
@@ -265,14 +265,14 @@ func (p *Provider) computeMergeBase(ctx context.Context, from, to string) string
 }
 
 func (p *Provider) workspaceTrackedDiff(ctx context.Context) (string, error) {
-	out, err := p.runGit(ctx, "diff", "--no-ext-diff", "--no-textconv", "HEAD", "--no-color", "-U"+fmt.Sprint(DiffContextLines), "--")
+	out, err := p.runGit(ctx, "diff", "--no-ext-diff", "--no-textconv", "--src-prefix=a/", "--dst-prefix=b/", "HEAD", "--no-color", "-U"+fmt.Sprint(DiffContextLines), "--")
 	if err == nil && out != "" {
 		return out, nil
 	}
 	if ctx.Err() != nil {
 		return "", ctx.Err()
 	}
-	return p.runGit(ctx, "diff", "--no-ext-diff", "--no-textconv", "--staged", "--no-color", "-U"+fmt.Sprint(DiffContextLines), "--")
+	return p.runGit(ctx, "diff", "--no-ext-diff", "--no-textconv", "--src-prefix=a/", "--dst-prefix=b/", "--staged", "--no-color", "-U"+fmt.Sprint(DiffContextLines), "--")
 }
 
 func (p *Provider) untrackedFileDiffs(ctx context.Context) ([]string, error) {
diff --git a/internal/diff/git_test.go b/internal/diff/git_test.go
index 7410857..b414b4e 100644
--- a/internal/diff/git_test.go
+++ b/internal/diff/git_test.go
@@ -97,6 +97,33 @@ func TestWorkspaceDiffSurvivesExternalDiffTool(t *testing.T) {
 	}
 }
 
+// TestCommitDiffSurvivesExternalDiffTool covers the ModeCommit call site
+// (git show <commit>), which likewise must pass --no-ext-diff so that a
+// user's external diff tool does not break single-commit analysis.
+func TestCommitDiffSurvivesExternalDiffTool(t *testing.T) {
+	repo := initRepoWithChange(t)
+
+	runGitTest(t, repo, "add", "sample.txt")
+	runGitTest(t, repo, "commit", "-q", "-m", "second commit")
+
+	garbage := writeGarbageExternalDiff(t)
+	t.Setenv("GIT_EXTERNAL_DIFF", garbage)
+
+	runner := gitcmd.New(0)
+	provider := NewCommitProvider(repo, "HEAD", runner)
+
+	diffs, err := provider.GetDiff(context.Background())
+	if err != nil {
+		t.Fatalf("GetDiff (commit) returned error: %v", err)
+	}
+
+	if len(diffs) == 0 {
+		t.Fatalf("expected at least one parsed commit diff with an external diff "+
+			"tool active, got 0 -- git show call site must pass "+
+			"--no-ext-diff (issue #82). GIT_EXTERNAL_DIFF=%s", garbage)
+	}
+}
+
 // TestRangeDiffSurvivesExternalDiffTool covers the ModeRange call site
 // (git diff <base> <to>), which likewise must pass --no-ext-diff so that a
 // user's external diff tool does not break range comparisons.