diff --git a/diff-lib.c b/diff-lib.c
index a680768ee7549a..6b14b9596299f1 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -701,7 +701,7 @@ int index_differs_from(struct repository *r,
 	return (has_changes != 0);
 }
 
-static struct strbuf *idiff_prefix_cb(struct diff_options *opt UNUSED, void *data)
+static const char *idiff_prefix_cb(struct diff_options *opt UNUSED, void *data)
 {
 	return data;
 }
@@ -716,7 +716,7 @@ void show_interdiff(const struct object_id *oid1, const struct object_id *oid2,
 	opts.output_format = DIFF_FORMAT_PATCH;
 	opts.output_prefix = idiff_prefix_cb;
 	strbuf_addchars(&prefix, ' ', indent);
-	opts.output_prefix_data = &prefix;
+	opts.output_prefix_data = prefix.buf;
 	diff_setup_done(&opts);
 
 	diff_tree_oid(oid1, oid2, "", &opts);
diff --git a/diff.c b/diff.c
index 173cbe2bed3501..3e4663ea5e2038 100644
--- a/diff.c
+++ b/diff.c
@@ -2317,12 +2317,10 @@ const char *diff_get_color(int diff_use_color, enum color_diff ix)
 
 const char *diff_line_prefix(struct diff_options *opt)
 {
-	struct strbuf *msgbuf;
-	if (!opt->output_prefix)
-		return "";
+	if (opt->output_prefix)
+		return opt->output_prefix(opt, opt->output_prefix_data);
 
-	msgbuf = opt->output_prefix(opt, opt->output_prefix_data);
-	return msgbuf->buf;
+	return "";
 }
 
 static unsigned long sane_truncate_line(char *line, unsigned long len)
diff --git a/diff.h b/diff.h
index 0cde3b34e23985..2a9c9191c1c9f9 100644
--- a/diff.h
+++ b/diff.h
@@ -94,7 +94,7 @@ typedef void (*add_remove_fn_t)(struct diff_options *options,
 typedef void (*diff_format_fn_t)(struct diff_queue_struct *q,
 		struct diff_options *options, void *data);
 
-typedef struct strbuf *(*diff_prefix_fn_t)(struct diff_options *opt, void *data);
+typedef const char *(*diff_prefix_fn_t)(struct diff_options *opt, void *data);
 
 #define DIFF_FORMAT_RAW		0x0001
 #define DIFF_FORMAT_DIFFSTAT	0x0002
diff --git a/graph.c b/graph.c
index 091c14cf4fbcf5..ebb7d1e66f4296 100644
--- a/graph.c
+++ b/graph.c
@@ -314,7 +314,7 @@ struct git_graph {
 	unsigned short default_column_color;
 };
 
-static struct strbuf *diff_output_prefix_callback(struct diff_options *opt, void *data)
+static const char *diff_output_prefix_callback(struct diff_options *opt, void *data)
 {
 	struct git_graph *graph = data;
 	static struct strbuf msgbuf = STRBUF_INIT;
@@ -327,7 +327,7 @@ static struct strbuf *diff_output_prefix_callback(struct diff_options *opt, void
 			   opt->line_prefix_length);
 	if (graph)
 		graph_padding_line(graph, &msgbuf);
-	return &msgbuf;
+	return msgbuf.buf;
 }
 
 static const struct diff_options *default_diffopt;
diff --git a/log-tree.c b/log-tree.c
index 3758e0d3b8e415..3af34b91a59513 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -923,10 +923,10 @@ int log_tree_diff_flush(struct rev_info *opt)
 			 */
 			int pch = DIFF_FORMAT_DIFFSTAT | DIFF_FORMAT_PATCH;
 			if (opt->diffopt.output_prefix) {
-				struct strbuf *msg = NULL;
+				const char *msg;
 				msg = opt->diffopt.output_prefix(&opt->diffopt,
 					opt->diffopt.output_prefix_data);
-				fwrite(msg->buf, msg->len, 1, opt->diffopt.file);
+				fwrite(msg, strlen(msg), 1, opt->diffopt.file);
 			}
 
 			/*
diff --git a/range-diff.c b/range-diff.c
index bbb0952264b817..10885ba3013897 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -480,7 +480,7 @@ static void patch_diff(const char *a, const char *b,
 	diff_flush(diffopt);
 }
 
-static struct strbuf *output_prefix_cb(struct diff_options *opt UNUSED, void *data)
+static const char *output_prefix_cb(struct diff_options *opt UNUSED, void *data)
 {
 	return data;
 }
@@ -508,7 +508,7 @@ static void output(struct string_list *a, struct string_list *b,
 	opts.flags.suppress_hunk_header_line_count = 1;
 	opts.output_prefix = output_prefix_cb;
 	strbuf_addstr(&indent, "    ");
-	opts.output_prefix_data = &indent;
+	opts.output_prefix_data = indent.buf;
 	diff_setup_done(&opts);
 
 	/*