diff --git a/core/include/gnuradio-4.0/Port.hpp b/core/include/gnuradio-4.0/Port.hpp
index 96ac0d0d..2dd30327 100644
--- a/core/include/gnuradio-4.0/Port.hpp
+++ b/core/include/gnuradio-4.0/Port.hpp
@@ -754,7 +754,7 @@ struct Port {
     template<PropertyMapType PropertyMap>
     inline constexpr void
     processPublishTag(PropertyMap &&tag_data, Tag::signed_index_type tagOffset) noexcept requires(kIsOutput) {
-        const auto newTagIndex = tagOffset < 0 ? tagOffset : streamWriter().position() + tagOffset;
+        const auto newTagIndex = tagOffset < 0 ? tagOffset : streamWriter().position() + 1 + tagOffset;
         fmt::print("publishing tag at {}, stream writer already published {} samples\n", newTagIndex, streamWriter().nSamplesPublished());
 
         if (isConnected() && tagOffset >= 0 && (_cachedTag.index != newTagIndex && _cachedTag.index != -1)) { // do not cache tags that have an explicit index
diff --git a/core/test/CMakeLists.txt b/core/test/CMakeLists.txt
index 44a1cafa..19badd35 100644
--- a/core/test/CMakeLists.txt
+++ b/core/test/CMakeLists.txt
@@ -36,6 +36,7 @@ add_ut_test(qa_DynamicPort)
 add_ut_test(qa_HierBlock)
 add_ut_test(qa_Block)
 add_ut_test(qa_LifeCycle)
+add_ut_test(qa_Port)
 add_ut_test(qa_Scheduler)
 add_ut_test(qa_reader_writer_lock)
 add_ut_test(qa_Settings)
diff --git a/core/test/qa_Port.cpp b/core/test/qa_Port.cpp
new file mode 100644
index 00000000..198a430b
--- /dev/null
+++ b/core/test/qa_Port.cpp
@@ -0,0 +1,114 @@
+#include <boost/ut.hpp>
+
+#include <fmt/format.h>
+#include <fmt/ranges.h>
+
+#include <gnuradio-4.0/Port.hpp>
+
+template<>
+struct fmt::formatter<gr::Tag> {
+    template<typename ParseContext>
+    constexpr auto
+    parse(ParseContext &ctx) {
+        return ctx.begin();
+    }
+
+    template<typename FormatContext>
+    constexpr auto
+    format(const gr::Tag &tag, FormatContext &ctx) const {
+        return fmt::format_to(ctx.out(), "  {}->{{ {} }}\n", tag.index, tag.map);
+    }
+};
+
+const boost::ut::suite PortTests = [] {
+    using namespace boost::ut;
+    using namespace gr;
+
+    "CustomSizePort"_test = [] {
+        PortOut<int, RequiredSamples<1, 16>, StreamBufferType<CircularBuffer<int, 32>>> out;
+        expect(out.resizeBuffer(32) == gr::ConnectionResult::SUCCESS);
+        expect(eq(out.buffer().streamBuffer.size(), static_cast<std::size_t>(getpagesize()))); // 4096 (page-size) is the minimum buffer size
+    };
+
+    "InputPort"_test = [] {
+        PortIn<int> in;
+        expect(eq(in.buffer().streamBuffer.size(), 65536UZ));
+
+        auto writer = in.buffer().streamBuffer.new_writer();
+        auto tagWriter = in.buffer().tagBuffer.new_writer();
+        { // put testdata into buffer
+            auto writeSpan = writer.reserve<SpanReleasePolicy::ProcessAll>(5);
+            auto tagSpan = tagWriter.reserve(3);
+            tagSpan[0] = {-1, {{"id", "tag@-1"}}};
+            tagSpan[1] = {1, {{"id", "tag@101"}}};
+            tagSpan[2] = {4, {{"id", "tag@104"}}};
+            std::ranges::iota(writeSpan, 100);
+            tagSpan.publish(3); // this should not be necessary as the ProcessAll policy should publish automatically
+            writeSpan.publish(5); // this should not be necessary as the ProcessAll policy should publish automatically
+        }
+        { // partial consume
+            auto data = in.get<SpanReleasePolicy::ProcessAll>(5);
+            expect(std::ranges::equal(data.tags, std::vector<gr::Tag>{ {-1, {{"id", "tag@-1"}}}, {1, {{"id", "tag@101"}}}, {4, {{"id", "tag@104"}}} }));
+            expect(std::ranges::equal(data, std::views::iota(100) | std::views::take(5)));
+            expect(data.consume(2));
+        }
+        { // full consume
+            auto data = in.get<SpanReleasePolicy::ProcessAll>(2);
+            expect(std::ranges::equal(data.tags, std::vector<gr::Tag>{ {1, {{"id", "tag@101"}}}} ));
+            expect(std::ranges::equal(data, std::views::iota(100) | std::views::drop(2) | std::views::take(2)));
+        }
+        { // get empty range
+            auto data = in.get<SpanReleasePolicy::ProcessAll>(0);
+            expect(std::ranges::equal(data.tags, std::vector<gr::Tag>{} ));
+            expect(std::ranges::equal(data, std::vector<int>()));
+        }
+    };
+
+    "OutputPort"_test = [] {
+        PortOut<int> out;
+        auto reader = out.buffer().streamBuffer.new_reader();
+        auto tagReader = out.buffer().tagBuffer.new_reader();
+        {
+            auto data = out.reserve<SpanReleasePolicy::ProcessAll>(5);
+            out.publishTag({{"id", "tag@-1"}}, -1);
+            out.publishPendingTags();
+            out.publishTag({{"id", "tag@101"}}, 1);
+            out.publishPendingTags();
+            out.publishTag({{"id", "tag@104"}}, 4);
+            out.publishPendingTags();
+            std::ranges::iota(data, 100);
+            out.publishPendingTags();
+            data.publish(5); // should be automatic
+        }
+        {
+            auto data = reader.get<SpanReleasePolicy::ProcessAll>();
+            auto tags = tagReader.get<SpanReleasePolicy::ProcessAll>();
+            expect(std::ranges::equal(data, std::views::iota(100) | std::views::take(5)));
+            // fmt::print("data: {}, tags: {}\n", std::span{data}, std::span{tags});
+            expect(std::ranges::equal(tags, std::vector<gr::Tag>{ { -1, {{"id", "tag@-1"}}}, {1, {{"id", "tag@101"}}}, {4, {{"id", "tag@104"}}} }));
+        }
+        {
+            auto data = out.reserve<SpanReleasePolicy::ProcessAll>(5);
+            out.publishTag({{"id", "tag@-1"}}, -1);
+            out.publishPendingTags();
+            out.publishTag({{"id", "tag@106"}}, 1);
+            out.publishPendingTags();
+            out.publishTag({{"id", "tag@109"}}, 4);
+            out.publishPendingTags();
+            std::ranges::iota(data, 105);
+            out.publishPendingTags();
+            data.publish(5); // should be automatic
+        }
+        {
+            auto data = reader.get();
+            auto tags = tagReader.get();
+            expect(std::ranges::equal(data, std::views::iota(105) | std::views::take(5)));
+            //fmt::print("data: {}, tags: {}\n", std::span{data}, std::span{tags});
+            expect(std::ranges::equal(tags, std::vector<gr::Tag>{ { -1, {{"id", "tag@-1"}}}, {6, {{"id", "tag@106"}}}, {9, {{"id", "tag@109"}}} }));
+        }
+    };
+};
+
+int
+main() { /* tests are statically executed */
+}