diff --git a/Makefile b/Makefile
index 42d11638b19..c1a1ce2c738 100644
--- a/Makefile
+++ b/Makefile
@@ -36,4 +36,4 @@ endif
 
 include mk/lib.mk
 
-GLOBAL_CXXFLAGS += -g -Wall -include config.h -std=c++20 -I src
+GLOBAL_CXXFLAGS += -g -Wall -include config.h -std=c++17 -I src
diff --git a/perl/Makefile b/perl/Makefile
index 2d759e6fc48..708f868822b 100644
--- a/perl/Makefile
+++ b/perl/Makefile
@@ -1,6 +1,6 @@
 makefiles = local.mk
 
-GLOBAL_CXXFLAGS += -g -Wall -std=c++20 -I ../src
+GLOBAL_CXXFLAGS += -g -Wall -std=c++17 -I ../src
 
 -include Makefile.config
 
diff --git a/src/libcmd/nix-cmd.pc.in b/src/libcmd/nix-cmd.pc.in
index a21d93f1d78..1761a9f418f 100644
--- a/src/libcmd/nix-cmd.pc.in
+++ b/src/libcmd/nix-cmd.pc.in
@@ -6,4 +6,4 @@ Name: Nix
 Description: Nix Package Manager
 Version: @PACKAGE_VERSION@
 Libs: -L${libdir} -lnixcmd
-Cflags: -I${includedir}/nix -std=c++20
+Cflags: -I${includedir}/nix -std=c++17
diff --git a/src/libexpr/nix-expr.pc.in b/src/libexpr/nix-expr.pc.in
index 95d452ca810..80f7a492b1a 100644
--- a/src/libexpr/nix-expr.pc.in
+++ b/src/libexpr/nix-expr.pc.in
@@ -7,4 +7,4 @@ Description: Nix Package Manager
 Version: @PACKAGE_VERSION@
 Requires: nix-store bdw-gc
 Libs: -L${libdir} -lnixexpr
-Cflags: -I${includedir}/nix -std=c++20
+Cflags: -I${includedir}/nix -std=c++17
diff --git a/src/libmain/nix-main.pc.in b/src/libmain/nix-main.pc.in
index b46ce199080..37b03dcd42c 100644
--- a/src/libmain/nix-main.pc.in
+++ b/src/libmain/nix-main.pc.in
@@ -6,4 +6,4 @@ Name: Nix
 Description: Nix Package Manager
 Version: @PACKAGE_VERSION@
 Libs: -L${libdir} -lnixmain
-Cflags: -I${includedir}/nix -std=c++20
+Cflags: -I${includedir}/nix -std=c++17
diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 751cf8c3088..05bf0501de6 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -370,7 +370,7 @@ void BinaryCacheStore::queryPathInfoUncached(const StorePath & storePath,
     auto callbackPtr = std::make_shared<decltype(callback)>(std::move(callback));
 
     getFile(narInfoFile,
-        {[=,this](std::future<std::optional<std::string>> fut) {
+        {[=](std::future<std::optional<std::string>> fut) {
             try {
                 auto data = fut.get();
 
diff --git a/src/libstore/build/worker.cc b/src/libstore/build/worker.cc
index f775f8486a0..b94fb841621 100644
--- a/src/libstore/build/worker.cc
+++ b/src/libstore/build/worker.cc
@@ -276,7 +276,7 @@ void Worker::run(const Goals & _topGoals)
         if (!children.empty() || !waitingForAWhile.empty())
             waitForInput();
         else {
-            if (awake.empty() && 0U == settings.maxBuildJobs)
+            if (awake.empty() && 0 == settings.maxBuildJobs)
             {
                 if (getMachines().empty())
                    throw Error("unable to start any build; either increase '--max-jobs' "
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index 8e33a3deca6..130c5b670b1 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -222,19 +222,19 @@ template<> void BaseSetting<SandboxMode>::convertToArg(Args & args, const std::s
         .longName = name,
         .description = "Enable sandboxing.",
         .category = category,
-        .handler = {[this]() { override(smEnabled); }}
+        .handler = {[=]() { override(smEnabled); }}
     });
     args.addFlag({
         .longName = "no-" + name,
         .description = "Disable sandboxing.",
         .category = category,
-        .handler = {[this]() { override(smDisabled); }}
+        .handler = {[=]() { override(smDisabled); }}
     });
     args.addFlag({
         .longName = "relaxed-" + name,
         .description = "Enable sandboxing, but allow builds to disable it.",
         .category = category,
-        .handler = {[this]() { override(smRelaxed); }}
+        .handler = {[=]() { override(smRelaxed); }}
     });
 }
 
diff --git a/src/libstore/nix-store.pc.in b/src/libstore/nix-store.pc.in
index 385169a1324..6d67b1e0380 100644
--- a/src/libstore/nix-store.pc.in
+++ b/src/libstore/nix-store.pc.in
@@ -6,4 +6,4 @@ Name: Nix
 Description: Nix Package Manager
 Version: @PACKAGE_VERSION@
 Libs: -L${libdir} -lnixstore -lnixutil
-Cflags: -I${includedir}/nix -std=c++20
+Cflags: -I${includedir}/nix -std=c++17
diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index 2930913d618..753980fd4ba 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -324,7 +324,7 @@ MultiCommand::MultiCommand(const Commands & commands_)
     expectArgs({
         .label = "subcommand",
         .optional = true,
-        .handler = {[=,this](std::string s) {
+        .handler = {[=](std::string s) {
             assert(!command);
             auto i = commands.find(s);
             if (i == commands.end()) {
diff --git a/src/libutil/config.cc b/src/libutil/config.cc
index b349f2d80ed..9bb412b4f5e 100644
--- a/src/libutil/config.cc
+++ b/src/libutil/config.cc
@@ -209,7 +209,7 @@ void BaseSetting<T>::convertToArg(Args & args, const std::string & category)
         .description = fmt("Set the `%s` setting.", name),
         .category = category,
         .labels = {"value"},
-        .handler = {[this](std::string s) { overridden = true; set(s); }},
+        .handler = {[=](std::string s) { overridden = true; set(s); }},
     });
 
     if (isAppendable())
@@ -218,7 +218,7 @@ void BaseSetting<T>::convertToArg(Args & args, const std::string & category)
             .description = fmt("Append to the `%s` setting.", name),
             .category = category,
             .labels = {"value"},
-            .handler = {[this](std::string s) { overridden = true; set(s, true); }},
+            .handler = {[=](std::string s) { overridden = true; set(s, true); }},
         });
 }
 
@@ -270,13 +270,13 @@ template<> void BaseSetting<bool>::convertToArg(Args & args, const std::string &
         .longName = name,
         .description = fmt("Enable the `%s` setting.", name),
         .category = category,
-        .handler = {[this]() { override(true); }}
+        .handler = {[=]() { override(true); }}
     });
     args.addFlag({
         .longName = "no-" + name,
         .description = fmt("Disable the `%s` setting.", name),
         .category = category,
-        .handler = {[this]() { override(false); }}
+        .handler = {[=]() { override(false); }}
     });
 }
 
diff --git a/src/libutil/config.hh b/src/libutil/config.hh
index 7ac43c85475..79ec0f9cf36 100644
--- a/src/libutil/config.hh
+++ b/src/libutil/config.hh
@@ -250,15 +250,11 @@ public:
     operator const T &() const { return value; }
     operator T &() { return value; }
     const T & get() const { return value; }
-    template<typename U>
-    bool operator ==(const U & v2) const { return value == v2; }
-    template<typename U>
-    bool operator !=(const U & v2) const { return value != v2; }
-    template<typename U>
-    void operator =(const U & v) { assign(v); }
+    bool operator ==(const T & v2) const { return value == v2; }
+    bool operator !=(const T & v2) const { return value != v2; }
+    void operator =(const T & v) { assign(v); }
     virtual void assign(const T & v) { value = v; }
-    template<typename U>
-    void setDefault(const U & v) { if (!overridden) value = v; }
+    void setDefault(const T & v) { if (!overridden) value = v; }
 
     void set(const std::string & str, bool append = false) override;