diff --git a/src/libexpr/flake/flakeref.cc b/src/libexpr/flake/flakeref.cc
index 930ed9ccd..c1eae413f 100644
--- a/src/libexpr/flake/flakeref.cc
+++ b/src/libexpr/flake/flakeref.cc
@@ -98,7 +98,7 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
     if (std::regex_match(url, match, flakeRegex)) {
         auto parsedURL = ParsedURL{
             .url = url,
-            .base = "flake:" + std::string(match[1]),
+            .base = "flake:" + match.str(1),
             .scheme = "flake",
             .authority = "",
             .path = match[1],
@@ -106,12 +106,12 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
 
         return std::make_pair(
             FlakeRef(Input::fromURL(parsedURL), ""),
-            percentDecode(std::string(match[6])));
+            percentDecode(match.str(6)));
     }
 
     else if (std::regex_match(url, match, pathUrlRegex)) {
         std::string path = match[1];
-        std::string fragment = percentDecode(std::string(match[3]));
+        std::string fragment = percentDecode(match.str(3));
 
         if (baseDir) {
             /* Check if 'url' is a path (either absolute or relative
diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index 255b42c49..c46262299 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -197,7 +197,7 @@ struct curlFileTransfer : public FileTransfer
                 result.etag = "";
                 result.data.clear();
                 result.bodySize = 0;
-                statusMsg = trim((std::string &) match[1]);
+                statusMsg = trim(match.str(1));
                 acceptRanges = false;
                 encoding = "";
             } else {
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 229bebbe6..b833038a9 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1263,9 +1263,9 @@ std::string chomp(std::string_view s)
 std::string trim(std::string_view s, std::string_view whitespace)
 {
     auto i = s.find_first_not_of(whitespace);
-    if (i == std::string_view::npos) return "";
+    if (i == s.npos) return "";
     auto j = s.find_last_not_of(whitespace);
-    return std::string(s, i, j == std::string::npos ? j : j - i + 1);
+    return std::string(s, i, j == s.npos ? j : j - i + 1);
 }
 
 
diff --git a/src/nix-channel/nix-channel.cc b/src/nix-channel/nix-channel.cc
index f46b90b90..cf52b03b4 100755
--- a/src/nix-channel/nix-channel.cc
+++ b/src/nix-channel/nix-channel.cc
@@ -96,7 +96,7 @@ static void update(const StringSet & channelNames)
         std::smatch match;
         auto urlBase = std::string(baseNameOf(url));
         if (std::regex_search(urlBase, match, std::regex("(-\\d.*)$")))
-            cname = cname + (std::string) match[1];
+            cname = cname + match.str(1);
 
         std::string extraAttrs;