diff --git a/include/osmium/area/detail/basic_assembler.hpp b/include/osmium/area/detail/basic_assembler.hpp
index 53f83011..4957fce0 100644
--- a/include/osmium/area/detail/basic_assembler.hpp
+++ b/include/osmium/area/detail/basic_assembler.hpp
@@ -217,7 +217,7 @@ namespace osmium {
                         }
                     }
 
-                    for (const osmium::Way* way : ways_in_multiple_rings) {
+                    for (const osmium::Way* way : ways_in_multiple_rings) { // NOLINT(bugprone-nondeterministic-pointer-iteration-order)
                         ++m_stats.ways_in_multiple_rings;
                         if (debug()) {
                             std::cerr << "      Way " << way->id() << " is in multiple rings\n";
diff --git a/include/osmium/experimental/flex_reader.hpp b/include/osmium/experimental/flex_reader.hpp
index 363b9e41..0e0aa9af 100644
--- a/include/osmium/experimental/flex_reader.hpp
+++ b/include/osmium/experimental/flex_reader.hpp
@@ -117,7 +117,7 @@ namespace osmium {
             }
 
             void close() {
-                return m_reader.close();
+                m_reader.close();
             }
 
             bool eof() const {
diff --git a/include/osmium/geom/tile.hpp b/include/osmium/geom/tile.hpp
index 1f5f1bfb..b4f6c2d1 100644
--- a/include/osmium/geom/tile.hpp
+++ b/include/osmium/geom/tile.hpp
@@ -47,7 +47,7 @@ namespace osmium {
         namespace detail {
 
             template <typename T>
-            inline constexpr const T& clamp(const T& value, const T& min, const T& max) {
+            inline constexpr const T clamp(const T value, const T min, const T max) {
                 return value < min ? min : (max < value ? max : value);
             }
 
diff --git a/include/osmium/io/reader_with_progress_bar.hpp b/include/osmium/io/reader_with_progress_bar.hpp
index 453f9f6e..2fda7563 100644
--- a/include/osmium/io/reader_with_progress_bar.hpp
+++ b/include/osmium/io/reader_with_progress_bar.hpp
@@ -91,7 +91,7 @@ namespace osmium {
         }
 
         inline InputIterator<ReaderWithProgressBar> end(ReaderWithProgressBar& /*reader*/) {
-            return InputIterator<ReaderWithProgressBar>();
+            return {};
         }
 
     } // namespace io
diff --git a/test/data-tests/testdata-multipolygon.cpp b/test/data-tests/testdata-multipolygon.cpp
index 1934d14b..bcf25fa6 100644
--- a/test/data-tests/testdata-multipolygon.cpp
+++ b/test/data-tests/testdata-multipolygon.cpp
@@ -31,6 +31,8 @@ struct less_charptr {
 
 using tagmap_type = std::map<const char*, const char*, less_charptr>;
 
+namespace {
+
 tagmap_type create_map(const osmium::TagList& taglist) {
     tagmap_type map;
 
@@ -41,6 +43,8 @@ tagmap_type create_map(const osmium::TagList& taglist) {
     return map;
 }
 
+} // anonymous namespace
+
 class TestHandler : public osmium::handler::Handler {
 
     gdalcpp::Layer m_layer_point;
diff --git a/test/data-tests/testdata-xml.cpp b/test/data-tests/testdata-xml.cpp
index 7cd4d159..1c997e18 100644
--- a/test/data-tests/testdata-xml.cpp
+++ b/test/data-tests/testdata-xml.cpp
@@ -17,18 +17,20 @@
 #include <iterator>
 #include <string>
 
-static std::string S_(const char* s) {
+namespace {
+
+std::string S_(const char* s) {
     return std::string{s};
 }
 
 // From C++20 we need to handle unicode literals differently
 #ifdef __cpp_char8_t
-static std::string S_(const char8_t* s) {
+std::string S_(const char8_t* s) {
     return std::string{reinterpret_cast<const char*>(s)};
 }
 #endif
 
-static std::string filename(const char* test_id, const char* suffix = "osm") {
+std::string filename(const char* test_id, const char* suffix = "osm") {
     const char* testdir = getenv("TESTDIR");
     if (!testdir) {
         throw std::runtime_error{"You have to set TESTDIR environment variable before running testdata-xml"};
@@ -56,7 +58,7 @@ struct header_buffer_type {
 // operations, because they make certain assumptions, for instance that
 // file contents fit into small buffers.
 
-static std::string read_file(const char* test_id) {
+std::string read_file(const char* test_id) {
     const int fd = osmium::io::detail::open_for_reading(filename(test_id));
     assert(fd >= 0);
 
@@ -70,7 +72,7 @@ static std::string read_file(const char* test_id) {
     return input;
 }
 
-static std::string read_gz_file(const char* test_id, const char* suffix) {
+std::string read_gz_file(const char* test_id, const char* suffix) {
     const int fd = osmium::io::detail::open_for_reading(filename(test_id, suffix));
     assert(fd >= 0);
 
@@ -81,7 +83,7 @@ static std::string read_gz_file(const char* test_id, const char* suffix) {
     return input;
 }
 
-static header_buffer_type parse_xml(std::string input) {
+header_buffer_type parse_xml(std::string input) {
     osmium::thread::Pool pool;
     osmium::io::detail::future_string_queue_type input_queue;
     osmium::io::detail::future_buffer_queue_type output_queue;
@@ -123,7 +125,7 @@ static header_buffer_type parse_xml(std::string input) {
     return result;
 }
 
-static header_buffer_type read_xml(const char* test_id) {
+header_buffer_type read_xml(const char* test_id) {
     const std::string input = read_file(test_id);
     return parse_xml(input);
 }
@@ -141,6 +143,8 @@ void test_fail(const char* xml_file_name, const char* errmsg) {
     }(), TException);
 }
 
+} // anonymous namespace
+
 // =============================================
 
 TEST_CASE("Reading OSM XML 100: Direct") {
diff --git a/test/t/geom/test_factory_with_projection.cpp b/test/t/geom/test_factory_with_projection.cpp
index 3d9923db..226ad9b4 100644
--- a/test/t/geom/test_factory_with_projection.cpp
+++ b/test/t/geom/test_factory_with_projection.cpp
@@ -6,7 +6,7 @@
 #include <string>
 
 TEST_CASE("Projection using MercatorProjection class to WKT") {
-    osmium::geom::WKTFactory<osmium::geom::MercatorProjection> factory{2};
+    const osmium::geom::WKTFactory<osmium::geom::MercatorProjection> factory{2};
 
     const std::string wkt{factory.create_point(osmium::Location{3.2, 4.2})};
     REQUIRE(wkt == "POINT(356222.37 467961.14)");