diff --git a/src/builtin_string.cpp b/src/builtin_string.cpp
index ef544c7da..3b4b17b6a 100644
--- a/src/builtin_string.cpp
+++ b/src/builtin_string.cpp
@@ -633,7 +633,7 @@ class wildcard_matcher_t : public string_matcher_t {
                        io_streams_t &streams)
         : string_matcher_t(opts, streams), wcpattern(parse_util_unescape_wildcards(pattern)) {
         if (opts.ignore_case) {
-            wcpattern = std::tolower(std::move(wcpattern));
+            wcpattern = wcstolower(std::move(wcpattern));
         }
         if (opts.entire) {
             if (!wcpattern.empty()) {
@@ -654,7 +654,7 @@ class wildcard_matcher_t : public string_matcher_t {
         bool match;
 
         if (opts.ignore_case) {
-            match = wildcard_match(std::tolower(arg), wcpattern, false);
+            match = wildcard_match(wcstolower(arg), wcpattern, false);
         } else {
             match = wildcard_match(arg, wcpattern, false);
         }
diff --git a/src/expand.h b/src/expand.h
index 40d4832c1..371724307 100644
--- a/src/expand.h
+++ b/src/expand.h
@@ -79,9 +79,9 @@ enum : wchar_t {
     VARIABLE_EXPAND,
     /// Character representing variable expansion into a single element.
     VARIABLE_EXPAND_SINGLE,
-    /// Character representing the start of a brace expansion.
+    /// Character representing the start of a bracket expansion.
     BRACE_BEGIN,
-    /// Character representing the end of a brace expansion.
+    /// Character representing the end of a bracket expansion.
     BRACE_END,
     /// Character representing separation between two bracket elements.
     BRACE_SEP,
diff --git a/src/history.cpp b/src/history.cpp
index 182e0b3b3..ea2bb5c1c 100644
--- a/src/history.cpp
+++ b/src/history.cpp
@@ -22,7 +22,6 @@
 #include <cwchar>
 #include <functional>
 #include <iterator>
-#include <locale>
 #include <map>
 #include <numeric>
 #include <type_traits>
@@ -181,7 +180,7 @@ bool history_item_t::matches_search(const wcstring &term, enum history_search_ty
     // search object if we're doing a case insensitive search.
     wcstring contents_lower;
     if (!case_sensitive) {
-        contents_lower = std::tolower(contents);
+        contents_lower = wcstolower(contents);
     }
     const wcstring &content_to_match = case_sensitive ? contents : contents_lower;
 
diff --git a/src/wcstringutil.cpp b/src/wcstringutil.cpp
index ea5f8b9a9..3691f79e5 100644
--- a/src/wcstringutil.cpp
+++ b/src/wcstringutil.cpp
@@ -4,6 +4,8 @@
 #include "common.h"
 #include "wcstringutil.h"
 
+#include <wctype.h>
+
 typedef wcstring::size_type size_type;
 
 wcstring_range wcstring_tok(wcstring &str, const wcstring &needle, wcstring_range last) {
@@ -62,3 +64,9 @@ wcstring trim(wcstring input, const wchar_t *any_of) {
     result.erase(0, prefix);
     return result;
 }
+
+wcstring wcstolower(wcstring input) {
+    wcstring result = std::move(input);
+    std::transform(result.begin(), result.end(), result.begin(), towlower);
+    return result;
+}
diff --git a/src/wcstringutil.h b/src/wcstringutil.h
index ee884b857..54ce9ba2a 100644
--- a/src/wcstringutil.h
+++ b/src/wcstringutil.h
@@ -68,4 +68,7 @@ wcstring truncate(const wcstring &input, int max_len,
 wcstring trim(wcstring input);
 wcstring trim(wcstring input, const wchar_t *any_of);
 
+/// Converts a string to lowercase.
+wcstring wcstolower(wcstring input);
+
 #endif