diff --git a/dev/tests/filesystem.lua b/dev/tests/filesystem.lua
index 38e7c4a04..cb5a052ac 100644
--- a/dev/tests/filesystem.lua
+++ b/dev/tests/filesystem.lua
@@ -1,3 +1,9 @@
+debug.log("file extension")
+asserts.equals(nil, file.ext("config:test"))
+asserts.equals("cfg", file.ext("config:test.cfg"))
+asserts.equals("gz", file.ext("config:test.cfg.gz"))
+asserts.equals("config:test.cfg", file.remove_ext("config:test.cfg.gz"))
+
 debug.log("check initial state")
 assert(file.exists("config:"))
 
diff --git a/res/modules/internal/extensions/file.lua b/res/modules/internal/extensions/file.lua
index d308eda9c..6d5dc30ba 100644
--- a/res/modules/internal/extensions/file.lua
+++ b/res/modules/internal/extensions/file.lua
@@ -8,7 +8,7 @@ function file.stem(path)
 end
 
 function file.ext(path)
-    return path:match("%.([^:/\\]+)$")
+    return path:match("[^:/\\.]%.([^.:/\\]+)$")
 end
 
 function file.prefix(path)
@@ -24,7 +24,11 @@ function file.parent(path)
 end
 
 function file.remove_ext(path)
-    return string.format("%s/%s", file.parent(path), file.stem(path))
+    local ext = file.ext(path)
+    if not ext then
+        return path
+    end
+    return path:sub(1, -#ext - 2)
 end
 
 function file.path(path)
diff --git a/src/util/stringutil.cpp b/src/util/stringutil.cpp
index 8d80a82ab..a2743a8ba 100644
--- a/src/util/stringutil.cpp
+++ b/src/util/stringutil.cpp
@@ -1,9 +1,11 @@
-#include "stringutil.hpp"
-
-#include <algorithm>
-#include <cmath>
-#include <iomanip>
-#include <locale>
+#include "stringutil.hpp"
+
+#include <algorithm>
+#include <charconv>
+#include <cctype>
+#include <cmath>
+#include <iomanip>
+#include <locale>
 #include <sstream>
 #include <stdexcept>
 
@@ -509,17 +511,22 @@ int util::replaceAll(
     return replace_all(str, from, to);
 }
 
-// replace it with std::from_chars in the far far future
-double util::parse_double(const std::string& str) {
-    std::istringstream ss(str);
-    ss.imbue(std::locale("C"));
-    double d;
-    ss >> d;
-    if (ss.fail()) {
-        throw std::runtime_error("invalid number format");
-    }
-    return d;
-}
+double util::parse_double(const std::string& str) {
+    const char* begin = str.data();
+    const char* end = begin + str.size();
+    while (begin != end && std::isspace(static_cast<unsigned char>(*begin))) {
+        begin++;
+    }
+    if (begin != end && *begin == '+') {
+        begin++;
+    }
+    double d = 0.0;
+    const auto result = std::from_chars(begin, end, d);
+    if (result.ec != std::errc()) {
+        throw std::runtime_error("invalid number format");
+    }
+    return d;
+}
 
 double util::parse_double(const std::string& str, size_t offset, size_t len) {
     return parse_double(str.substr(offset, len));
diff --git a/test/util/stringutil.cpp b/test/util/stringutil.cpp
index a057d4e69..88915c58d 100644
--- a/test/util/stringutil.cpp
+++ b/test/util/stringutil.cpp
@@ -68,6 +68,14 @@ TEST(stringutil, base64_urlsafe) {
     }
 }
 
+TEST(stringutil, parse_double) {
+    EXPECT_DOUBLE_EQ(util::parse_double("53.125"), 53.125);
+    EXPECT_DOUBLE_EQ(util::parse_double("-0.25"), -0.25);
+    EXPECT_DOUBLE_EQ(util::parse_double("  +12.5"), 12.5);
+    EXPECT_DOUBLE_EQ(util::parse_double("xx1.75yy", 2, 4), 1.75);
+    EXPECT_THROW(util::parse_double("not-a-number"), std::runtime_error);
+}
+
 class StringParser : BasicParser<char> {
 public:
     StringParser(std::string_view source) : BasicParser("<string>", source) {}