diff --git a/src/libcmd/command.cc b/src/libcmd/command.cc
index a88ba81340d..de9f546fc70 100644
--- a/src/libcmd/command.cc
+++ b/src/libcmd/command.cc
@@ -175,7 +175,7 @@ void BuiltPathsCommand::run(ref<Store> store, Installables && installables)
             throw UsageError("'--all' does not expect arguments");
         // XXX: Only uses opaque paths, ignores all the realisations
         for (auto & p : store->queryAllValidPaths())
-            paths.push_back(BuiltPath::Opaque{p});
+            paths.emplace_back(BuiltPath::Opaque{p});
     } else {
         paths = Installable::toBuiltPaths(getEvalStore(), store, realiseMode, operateOn, installables);
         if (recursive) {
@@ -188,7 +188,7 @@ void BuiltPathsCommand::run(ref<Store> store, Installables && installables)
             }
             store->computeFSClosure(pathsRoots, pathsClosure);
             for (auto & path : pathsClosure)
-                paths.push_back(BuiltPath::Opaque{path});
+                paths.emplace_back(BuiltPath::Opaque{path});
         }
     }
 
diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index 3aff601e002..bc0b8a9881e 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -663,7 +663,7 @@ BuiltPaths Installable::toBuiltPaths(
 
         BuiltPaths res;
         for (auto & drvPath : Installable::toDerivations(store, installables, true))
-            res.push_back(BuiltPath::Opaque{drvPath});
+            res.emplace_back(BuiltPath::Opaque{drvPath});
         return res;
     }
 }
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index efdad18e180..1fecd1c97b6 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -352,7 +352,7 @@ Derivation parseDerivation(
         expect(str, "erive(");
         version = DerivationATermVersion::Traditional;
         break;
-    case 'r':
+    case 'r': {
         expect(str, "rvWithVersion(");
         auto versionS = parseString(str);
         if (versionS == "xp-dyn-drv") {
@@ -365,6 +365,9 @@ Derivation parseDerivation(
         expect(str, ",");
         break;
     }
+    default:
+        throw Error("derivation does not start with 'Derive' or 'DrvWithVersion'");
+    }
 
     /* Parse the list of outputs. */
     expect(str, "[");
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index ac96e8bb14a..646b0ec7da7 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -819,7 +819,7 @@ void Store::substitutePaths(const StorePathSet & paths)
     std::vector<DerivedPath> paths2;
     for (auto & path : paths)
         if (!path.isDerivation())
-            paths2.push_back(DerivedPath::Opaque{path});
+            paths2.emplace_back(DerivedPath::Opaque{path});
     uint64_t downloadSize, narSize;
     StorePathSet willBuild, willSubstitute, unknown;
     queryMissing(paths2,
diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index e62c4f6b130..60bc0814618 100644
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -449,7 +449,7 @@ static void main_nix_build(int argc, char * * argv)
             }
         }
         for (const auto & src : drv.inputSrcs) {
-            pathsToBuild.push_back(DerivedPath::Opaque{src});
+            pathsToBuild.emplace_back(DerivedPath::Opaque{src});
             pathsToCopy.insert(src);
         }
 
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index 01742daa8d9..25068f80114 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -481,12 +481,12 @@ static void printMissing(EvalState & state, DrvInfos & elems)
     std::vector<DerivedPath> targets;
     for (auto & i : elems)
         if (auto drvPath = i.queryDrvPath())
-            targets.push_back(DerivedPath::Built{
+            targets.emplace_back(DerivedPath::Built{
                 .drvPath = makeConstantStorePathRef(*drvPath),
                 .outputs = OutputsSpec::All { },
             });
         else
-            targets.push_back(DerivedPath::Opaque{
+            targets.emplace_back(DerivedPath::Opaque{
                 .path = i.queryOutPath(),
             });