diff --git a/src/locale/__setlocalecat.c b/src/locale/__setlocalecat.c
index c93e9ba0de0334da84a382e942274456cee090d7..e829da56759b5ae7f42132abb6d48e37c9d97dfc 100644
--- a/src/locale/__setlocalecat.c
+++ b/src/locale/__setlocalecat.c
@@ -17,8 +17,9 @@ char *__strchrnul(const char *, int);
 
 static struct __locale_map *findlocale(const char *name, size_t n)
 {
+	static int lock[2];
 	static void *volatile loc_head;
-	struct __locale_map *p, *new, *old_head;
+	struct __locale_map *p, *new = 0;
 	const char *path = 0, *z;
 	char buf[256];
 	size_t l;
@@ -28,11 +29,18 @@ static struct __locale_map *findlocale(const char *name, size_t n)
 	for (p=loc_head; p; p=p->next)
 		if (!strcmp(name, p->name)) return p;
 
+	LOCK(lock);
+
+	for (p=loc_head; p; p=p->next)
+		if (!strcmp(name, p->name)) {
+			UNLOCK(lock);
+			return p;
+		}
+
 	if (!libc.secure) path = getenv("MUSL_LOCPATH");
 	/* FIXME: add a default path? */
-	if (!path) return 0;
 
-	for (; *path; path=z+!!*z) {
+	if (path) for (; *path; path=z+!!*z) {
 		z = __strchrnul(path, ':');
 		l = z - path - !!*z;
 		if (l >= sizeof buf - n - 2) continue;
@@ -45,20 +53,19 @@ static struct __locale_map *findlocale(const char *name, size_t n)
 			new = malloc(sizeof *new);
 			if (!new) {
 				__munmap((void *)map, map_size);
-				return 0;
+				break;
 			}
 			new->map = map;
 			new->map_size = map_size;
 			memcpy(new->name, name, n);
 			new->name[n] = 0;
-			do {
-				old_head = loc_head;
-				new->next = old_head;
-			} while (a_cas_p(&loc_head, old_head, new) != old_head);
-			return new;
+			new->next = loc_head;
+			loc_head = new;
+			break;
 		}
 	}
-	return 0;
+	UNLOCK(lock);
+	return new;
 }
 
 static const char envvars[][12] = {
@@ -85,11 +92,10 @@ int __setlocalecat(locale_t loc, int cat, const char *val)
 	int builtin = (val[0]=='C' && !val[1])
 		|| !strcmp(val, "C.UTF-8")
 		|| !strcmp(val, "POSIX");
-	struct __locale_map *data, *old;
 
 	switch (cat) {
 	case LC_CTYPE:
-		a_store(&loc->ctype_utf8, !builtin || val[1]=='.');
+		loc->ctype_utf8 = !builtin || val[1]=='.';
 		break;
 	case LC_MESSAGES:
 		if (builtin) {
@@ -100,10 +106,7 @@ int __setlocalecat(locale_t loc, int cat, const char *val)
 		}
 		/* fall through */
 	default:
-		data = builtin ? 0 : findlocale(val, n);
-		if (data == loc->cat[cat-2]) break;
-		do old = loc->cat[cat-2];
-		while (a_cas_p(&loc->cat[cat-2], old, data) != old);
+		loc->cat[cat-2] = builtin ? 0 : findlocale(val, n);
 	case LC_NUMERIC:
 		break;
 	}
diff --git a/src/locale/setlocale.c b/src/locale/setlocale.c
index d797f43fe8855c3393fb41b965eaefabb578542c..32a8fcab5fde043654ed06a16820f9464bce1981 100644
--- a/src/locale/setlocale.c
+++ b/src/locale/setlocale.c
@@ -7,8 +7,29 @@
 
 static char buf[2+4*(LOCALE_NAME_MAX+1)];
 
+static char *setlocale_one_unlocked(int cat, const char *name)
+{
+	struct __locale_map *lm;
+
+	if (name) __setlocalecat(&libc.global_locale, cat, name);
+
+	switch (cat) {
+	case LC_CTYPE:
+		return libc.global_locale.ctype_utf8 ? "C.UTF-8" : "C";
+	case LC_NUMERIC:
+		return "C";
+	case LC_MESSAGES:
+		return libc.global_locale.messages_name[0]
+			? libc.global_locale.messages_name : "C";
+	default:
+		lm = libc.global_locale.cat[cat-2];
+		return lm ? lm->name : "C";
+	}
+}
+
 char *setlocale(int cat, const char *name)
 {
+	static volatile int lock[2];
 	struct __locale_map *lm;
 	int i, j;
 
@@ -19,6 +40,8 @@ char *setlocale(int cat, const char *name)
 
 	if ((unsigned)cat > LC_ALL) return 0;
 
+	LOCK(lock);
+
 	/* For LC_ALL, setlocale is required to return a string which
 	 * encodes the current setting for all categories. The format of
 	 * this string is unspecified, and only the following code, which
@@ -37,12 +60,13 @@ char *setlocale(int cat, const char *name)
 					memcpy(part, name + 2 + (i-2)*(LOCALE_NAME_MAX+1), LOCALE_NAME_MAX);
 					for (j=LOCALE_NAME_MAX-1; j && part[j]==';'; j--)
 						part[j] = 0;
-					setlocale(i, part);
+					setlocale_one_unlocked(i, part);
 				}
-				setlocale(LC_MESSAGES, name + 2 + 3*(LOCALE_NAME_MAX+1));
+				setlocale_one_unlocked(LC_MESSAGES, name
+					+ 2 + 3*(LOCALE_NAME_MAX+1));
 			} else {
 				for (i=0; i<LC_ALL; i++)
-					setlocale(i, name);
+					setlocale_one_unlocked(i, name);
 			}
 		}
 		memset(buf, ';', 2 + 3*(LOCALE_NAME_MAX+1));
@@ -52,21 +76,13 @@ char *setlocale(int cat, const char *name)
 			if (lm) memcpy(buf + 2 + (i-2)*(LOCALE_NAME_MAX+1),
 				lm->name, strlen(lm->name));
 		}
+		UNLOCK(lock);
 		return buf;
 	}
 
-	if (name) __setlocalecat(&libc.global_locale, cat, name);
+	char *ret = setlocale_one_unlocked(cat, name);
 
-	switch (cat) {
-	case LC_CTYPE:
-		return libc.global_locale.ctype_utf8 ? "C.UTF-8" : "C";
-	case LC_NUMERIC:
-		return "C";
-	case LC_MESSAGES:
-		return libc.global_locale.messages_name[0]
-			? libc.global_locale.messages_name : "C";
-	default:
-		lm = libc.global_locale.cat[cat-2];
-		return lm ? lm->name : "C";
-	}
+	UNLOCK(lock);
+
+	return ret;
 }