diff --git a/config.c b/config.c
index fb56e11276..f9101045ee 100644
--- a/config.c
+++ b/config.c
@@ -1564,8 +1564,10 @@ static int git_default_core_config(const char *var, const char *value,
 		return 0;
 	}
 
-	if (!strcmp(var, "core.checkroundtripencoding"))
-		return git_config_string(&check_roundtrip_encoding, var, value);
+	if (!strcmp(var, "core.checkroundtripencoding")) {
+		FREE_AND_NULL(check_roundtrip_encoding);
+		return git_config_string((const char **) &check_roundtrip_encoding, var, value);
+	}
 
 	if (!strcmp(var, "core.notesref")) {
 		if (!value)
diff --git a/convert.c b/convert.c
index 35b25eb3cb..03c3c528f9 100644
--- a/convert.c
+++ b/convert.c
@@ -345,30 +345,32 @@ static int check_roundtrip(const char *enc_name)
 	 * space separated encodings (eg. "UTF-16, ASCII, CP1125").
 	 * Search for the given encoding in that string.
 	 */
-	const char *found = strcasestr(check_roundtrip_encoding, enc_name);
+	const char *encoding = check_roundtrip_encoding ?
+		check_roundtrip_encoding : "SHIFT-JIS";
+	const char *found = strcasestr(encoding, enc_name);
 	const char *next;
 	int len;
 	if (!found)
 		return 0;
 	next = found + strlen(enc_name);
-	len = strlen(check_roundtrip_encoding);
+	len = strlen(encoding);
 	return (found && (
 			/*
-			 * check that the found encoding is at the
-			 * beginning of check_roundtrip_encoding or
-			 * that it is prefixed with a space or comma
+			 * Check that the found encoding is at the beginning of
+			 * encoding or that it is prefixed with a space or
+			 * comma.
 			 */
-			found == check_roundtrip_encoding || (
+			found == encoding || (
 				(isspace(found[-1]) || found[-1] == ',')
 			)
 		) && (
 			/*
-			 * check that the found encoding is at the
-			 * end of check_roundtrip_encoding or
-			 * that it is suffixed with a space or comma
+			 * Check that the found encoding is at the end of
+			 * encoding or that it is suffixed with a space
+			 * or comma.
 			 */
-			next == check_roundtrip_encoding + len || (
-				next < check_roundtrip_encoding + len &&
+			next == encoding + len || (
+				next < encoding + len &&
 				(isspace(next[0]) || next[0] == ',')
 			)
 		));
diff --git a/convert.h b/convert.h
index ab8b4fa68d..d925589444 100644
--- a/convert.h
+++ b/convert.h
@@ -92,7 +92,7 @@ void convert_attrs(struct index_state *istate,
 		   struct conv_attrs *ca, const char *path);
 
 extern enum eol core_eol;
-extern const char *check_roundtrip_encoding;
+extern char *check_roundtrip_encoding;
 const char *get_cached_convert_stats_ascii(struct index_state *istate,
 					   const char *path);
 const char *get_wt_convert_stats_ascii(const char *path);
diff --git a/environment.c b/environment.c
index 279ea3fd5e..ab6956559e 100644
--- a/environment.c
+++ b/environment.c
@@ -64,7 +64,7 @@ char *excludes_file;
 enum auto_crlf auto_crlf = AUTO_CRLF_FALSE;
 enum eol core_eol = EOL_UNSET;
 int global_conv_flags_eol = CONV_EOL_RNDTRP_WARN;
-const char *check_roundtrip_encoding = "SHIFT-JIS";
+char *check_roundtrip_encoding;
 enum branch_track git_branch_track = BRANCH_TRACK_REMOTE;
 enum rebase_setup_type autorebase = AUTOREBASE_NEVER;
 enum push_default_type push_default = PUSH_DEFAULT_UNSPECIFIED;