diff --git a/abspath.c b/abspath.c
index fd30aff08fdae93ecb7283b4e145cab41fd2f9c9..c6f480993d7cb404ac5d275db86be6f64a325a6b 100644
--- a/abspath.c
+++ b/abspath.c
@@ -246,9 +246,11 @@ char *absolute_pathdup(const char *path)
 	return strbuf_detach(&sb, NULL);
 }
 
-const char *prefix_filename(const char *pfx, int pfx_len, const char *arg)
+const char *prefix_filename(const char *pfx, const char *arg)
 {
 	static struct strbuf path = STRBUF_INIT;
+	size_t pfx_len = pfx ? strlen(pfx) : 0;
+
 #ifndef GIT_WINDOWS_NATIVE
 	if (!pfx_len || is_absolute_path(arg))
 		return arg;
diff --git a/apply.c b/apply.c
index 0e2caeab9cc523364e0cfbb8cbbb5aba1a0a58ee..b8bd5a4befa410ffa96ea638c2eb59f51c2b2c96 100644
--- a/apply.c
+++ b/apply.c
@@ -2046,7 +2046,7 @@ static void prefix_one(struct apply_state *state, char **name)
 	char *old_name = *name;
 	if (!old_name)
 		return;
-	*name = xstrdup(prefix_filename(state->prefix, state->prefix_length, *name));
+	*name = xstrdup(prefix_filename(state->prefix, *name));
 	free(old_name);
 }
 
@@ -4815,9 +4815,7 @@ int apply_all_patches(struct apply_state *state,
 			read_stdin = 0;
 			continue;
 		} else if (0 < state->prefix_length)
-			arg = prefix_filename(state->prefix,
-					      state->prefix_length,
-					      arg);
+			arg = prefix_filename(state->prefix, arg);
 
 		fd = open(arg, O_RDONLY);
 		if (fd < 0) {
diff --git a/builtin/config.c b/builtin/config.c
index 05843a0f96e4dc0dbf9fbc7310039794b57947e7..74f6c34d11ec720b7faf8212b9b61ec0648cf4aa 100644
--- a/builtin/config.c
+++ b/builtin/config.c
@@ -528,7 +528,6 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 		if (!is_absolute_path(given_config_source.file) && prefix)
 			given_config_source.file =
 				xstrdup(prefix_filename(prefix,
-							strlen(prefix),
 							given_config_source.file));
 	}
 
diff --git a/builtin/hash-object.c b/builtin/hash-object.c
index 56df77b0c2a299fcba56a2542f7adb34869ced9f..2ea36909d2443dc704c035d57840f804fb6f6401 100644
--- a/builtin/hash-object.c
+++ b/builtin/hash-object.c
@@ -102,7 +102,6 @@ int cmd_hash_object(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 	int i;
-	int prefix_length = -1;
 	const char *errstr = NULL;
 
 	argc = parse_options(argc, argv, NULL, hash_object_options,
@@ -113,9 +112,8 @@ int cmd_hash_object(int argc, const char **argv, const char *prefix)
 	else
 		prefix = setup_git_directory_gently(&nongit);
 
-	prefix_length = prefix ? strlen(prefix) : 0;
 	if (vpath && prefix)
-		vpath = xstrdup(prefix_filename(prefix, prefix_length, vpath));
+		vpath = xstrdup(prefix_filename(prefix, vpath));
 
 	git_config(git_default_config, NULL);
 
@@ -146,9 +144,8 @@ int cmd_hash_object(int argc, const char **argv, const char *prefix)
 		const char *arg = argv[i];
 		char *to_free = NULL;
 
-		if (0 <= prefix_length)
-			arg = to_free =
-				xstrdup(prefix_filename(prefix, prefix_length, arg));
+		if (prefix)
+			arg = to_free = xstrdup(prefix_filename(prefix, arg));
 		hash_object(arg, type, no_filters ? NULL : vpath ? vpath : arg,
 			    flags, literally);
 		free(to_free);
diff --git a/builtin/log.c b/builtin/log.c
index 281af8c1ecb04c7be05d9a17a1d5f3bd43420c85..bfdc7a23d36473a271a1296b67ed0c850407c6bc 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1084,8 +1084,7 @@ static const char *set_outdir(const char *prefix, const char *output_directory)
 	if (!output_directory)
 		return prefix;
 
-	return xstrdup(prefix_filename(prefix, outdir_offset,
-				       output_directory));
+	return xstrdup(prefix_filename(prefix, output_directory));
 }
 
 static const char * const builtin_format_patch_usage[] = {
diff --git a/builtin/mailinfo.c b/builtin/mailinfo.c
index e3b62f2fc744d340de5e3d9efad12b5de93cd55c..681f07f54d792af1be9fe9ed4636d8ce947cd75b 100644
--- a/builtin/mailinfo.c
+++ b/builtin/mailinfo.c
@@ -15,7 +15,7 @@ static char *prefix_copy(const char *prefix, const char *filename)
 {
 	if (!prefix || is_absolute_path(filename))
 		return xstrdup(filename);
-	return xstrdup(prefix_filename(prefix, strlen(prefix), filename));
+	return xstrdup(prefix_filename(prefix, filename));
 }
 
 int cmd_mailinfo(int argc, const char **argv, const char *prefix)
diff --git a/builtin/merge-file.c b/builtin/merge-file.c
index 13e22a2f0be73ec7e521a02d1f36c414e77a8700..63cd94358770326e109df8f2b628aa6b8c97bc40 100644
--- a/builtin/merge-file.c
+++ b/builtin/merge-file.c
@@ -28,7 +28,6 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
 	xmparam_t xmp = {{0}};
 	int ret = 0, i = 0, to_stdout = 0;
 	int quiet = 0;
-	int prefixlen = 0;
 	struct option options[] = {
 		OPT_BOOL('p', "stdout", &to_stdout, N_("send results to standard output")),
 		OPT_SET_INT(0, "diff3", &xmp.style, N_("use a diff3 based merge"), XDL_MERGE_DIFF3),
@@ -65,11 +64,8 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
 			return error_errno("failed to redirect stderr to /dev/null");
 	}
 
-	if (prefix)
-		prefixlen = strlen(prefix);
-
 	for (i = 0; i < 3; i++) {
-		const char *fname = prefix_filename(prefix, prefixlen, argv[i]);
+		const char *fname = prefix_filename(prefix, argv[i]);
 		if (!names[i])
 			names[i] = argv[i];
 		if (read_mmfile(mmfs + i, fname))
@@ -90,7 +86,7 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
 
 	if (ret >= 0) {
 		const char *filename = argv[0];
-		const char *fpath = prefix_filename(prefix, prefixlen, argv[0]);
+		const char *fpath = prefix_filename(prefix, argv[0]);
 		FILE *f = to_stdout ? stdout : fopen(fpath, "wb");
 
 		if (!f)
diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index 2549643267440c5742690e3b808943de6fad19af..c8035331e21579df39c6a76aca8a8299c6b9b5df 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -228,9 +228,7 @@ static int show_file(const char *arg, int output_prefix)
 	if ((filter & (DO_NONFLAGS|DO_NOREV)) == (DO_NONFLAGS|DO_NOREV)) {
 		if (output_prefix) {
 			const char *prefix = startup_info->prefix;
-			show(prefix_filename(prefix,
-					     prefix ? strlen(prefix) : 0,
-					     arg));
+			show(prefix_filename(prefix, arg));
 		} else
 			show(arg);
 		return 1;
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 831fe058a53da95643b1a93038f576d5bffea7ef..e38325e44bb567a63b622418a573f2296c91eea3 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -338,7 +338,7 @@ static int add(int ac, const char **av, const char *prefix)
 	if (ac < 1 || ac > 2)
 		usage_with_options(worktree_usage, options);
 
-	path = prefix_filename(prefix, strlen(prefix), av[0]);
+	path = prefix_filename(prefix, av[0]);
 	branch = ac < 2 ? "HEAD" : av[1];
 
 	if (!strcmp(branch, "-"))
diff --git a/cache.h b/cache.h
index a01668fc42e72815489b552f8960118353f2cfd1..0b53aef0ed4b761aed47e8e930e1237666bac287 100644
--- a/cache.h
+++ b/cache.h
@@ -540,7 +540,7 @@ extern char *prefix_path_gently(const char *prefix, int len, int *remaining, con
  * The return value may point to static storage which will be overwritten by
  * further calls.
  */
-extern const char *prefix_filename(const char *prefix, int len, const char *path);
+extern const char *prefix_filename(const char *prefix, const char *path);
 
 extern int check_filename(const char *prefix, const char *name);
 extern void verify_filename(const char *prefix,
diff --git a/diff-no-index.c b/diff-no-index.c
index df762fd0f7d1ec74175a42de07b064107d3a601a..5f7317ced9ec1ab06d61d04fdb2c3526d794249a 100644
--- a/diff-no-index.c
+++ b/diff-no-index.c
@@ -236,7 +236,7 @@ static void fixup_paths(const char **path, struct strbuf *replacement)
 void diff_no_index(struct rev_info *revs,
 		   int argc, const char **argv)
 {
-	int i, prefixlen;
+	int i;
 	const char *paths[2];
 	struct strbuf replacement = STRBUF_INIT;
 	const char *prefix = revs->prefix;
@@ -257,7 +257,6 @@ void diff_no_index(struct rev_info *revs,
 		}
 	}
 
-	prefixlen = prefix ? strlen(prefix) : 0;
 	for (i = 0; i < 2; i++) {
 		const char *p = argv[argc - 2 + i];
 		if (!strcmp(p, "-"))
@@ -266,8 +265,8 @@ void diff_no_index(struct rev_info *revs,
 			 * path that is "-", spell it as "./-".
 			 */
 			p = file_from_standard_input;
-		else if (prefixlen)
-			p = xstrdup(prefix_filename(prefix, prefixlen, p));
+		else if (prefix)
+			p = xstrdup(prefix_filename(prefix, p));
 		paths[i] = p;
 	}
 
diff --git a/diff.c b/diff.c
index a628ac3a95108ca79aef0b41b7051ab2fcbe693a..70870b4b6963d55472b7f9c6232f9a194bddd83a 100644
--- a/diff.c
+++ b/diff.c
@@ -4023,7 +4023,7 @@ int diff_opt_parse(struct diff_options *options,
 	else if (!strcmp(arg, "--pickaxe-regex"))
 		options->pickaxe_opts |= DIFF_PICKAXE_REGEX;
 	else if ((argcount = short_opt('O', av, &optarg))) {
-		const char *path = prefix_filename(prefix, strlen(prefix), optarg);
+		const char *path = prefix_filename(prefix, optarg);
 		options->orderfile = xstrdup(path);
 		return argcount;
 	}
@@ -4071,7 +4071,7 @@ int diff_opt_parse(struct diff_options *options,
 	else if (!strcmp(arg, "--no-function-context"))
 		DIFF_OPT_CLR(options, FUNCCONTEXT);
 	else if ((argcount = parse_long_opt("output", av, &optarg))) {
-		const char *path = prefix_filename(prefix, strlen(prefix), optarg);
+		const char *path = prefix_filename(prefix, optarg);
 		options->file = fopen(path, "w");
 		if (!options->file)
 			die_errno("Could not open '%s'", path);
diff --git a/parse-options.c b/parse-options.c
index 4fbe924a5de27d04b271a11a2ae040e817483951..ba6cc30b26aebdcd1a9a14b6e7a2ad4a481ab128 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -40,7 +40,7 @@ static void fix_filename(const char *prefix, const char **file)
 	if (!file || !*file || !prefix || is_absolute_path(*file)
 	    || !strcmp("-", *file))
 		return;
-	*file = xstrdup(prefix_filename(prefix, strlen(prefix), *file));
+	*file = xstrdup(prefix_filename(prefix, *file));
 }
 
 static int opt_command_mode_error(const struct option *opt,
diff --git a/setup.c b/setup.c
index 64f922a9378cc48c72b9173e7c45296bdb885678..a76379e0ceaa688322da8f07c02350cfbcba7ccf 100644
--- a/setup.c
+++ b/setup.c
@@ -142,7 +142,7 @@ int check_filename(const char *prefix, const char *arg)
 			return 1;
 		name = arg + 2;
 	} else if (prefix)
-		name = prefix_filename(prefix, strlen(prefix), arg);
+		name = prefix_filename(prefix, arg);
 	else
 		name = arg;
 	if (!lstat(name, &st))
diff --git a/worktree.c b/worktree.c
index fa7bc67a50a6d52116b0ca994b473668998f1c3f..42dd3d52b0963445a304062feaba79a64ecca0ef 100644
--- a/worktree.c
+++ b/worktree.c
@@ -254,7 +254,7 @@ struct worktree *find_worktree(struct worktree **list,
 	if ((wt = find_worktree_by_suffix(list, arg)))
 		return wt;
 
-	arg = prefix_filename(prefix, strlen(prefix), arg);
+	arg = prefix_filename(prefix, arg);
 	path = real_pathdup(arg, 1);
 	for (; *list; list++)
 		if (!fspathcmp(path, real_path((*list)->path)))