diff --git a/src/network/access/http2/hpack.cpp b/src/network/access/http2/hpack.cpp
index d859affd7c3..f6c7c9d69e1 100644
--- a/src/network/access/http2/hpack.cpp
+++ b/src/network/access/http2/hpack.cpp
@@ -111,6 +111,16 @@ quint32 Encoder::dynamicTableSize() const
     return lookupTable.dynamicDataSize();
 }
 
+quint32 Encoder::dynamicTableCapacity() const
+{
+    return lookupTable.dynamicDataCapacity();
+}
+
+quint32 Encoder::maxDynamicTableCapacity() const
+{
+    return lookupTable.maxDynamicDataCapacity();
+}
+
 bool Encoder::encodeRequest(BitOStream &outputStream, const HttpHeader &header)
 {
     if (!header.size()) {
@@ -408,6 +418,16 @@ quint32 Decoder::dynamicTableSize() const
     return lookupTable.dynamicDataSize();
 }
 
+quint32 Decoder::dynamicTableCapacity() const
+{
+    return lookupTable.dynamicDataCapacity();
+}
+
+quint32 Decoder::maxDynamicTableCapacity() const
+{
+    return lookupTable.maxDynamicDataCapacity();
+}
+
 void Decoder::setMaxDynamicTableSize(quint32 size)
 {
     // Up to a caller (HTTP2 protocol handler)
@@ -491,6 +511,11 @@ bool Decoder::processDecodedField(BitPattern fieldType,
             return false;
     }
 
+    if (lookupTable.maxDynamicDataCapacity() < lookupTable.dynamicDataCapacity()) {
+        qDebug("about to add a new field, but expected a Dynamic Table Size Update");
+        return false; // We expected a dynamic table size update.
+    }
+
     header.push_back(HeaderField(name, value));
     return true;
 }
diff --git a/src/network/access/http2/hpack_p.h b/src/network/access/http2/hpack_p.h
index aecaf5467e4..56162e340ac 100644
--- a/src/network/access/http2/hpack_p.h
+++ b/src/network/access/http2/hpack_p.h
@@ -38,6 +38,8 @@ public:
     Encoder(quint32 maxTableSize, bool compressStrings);
 
     quint32 dynamicTableSize() const;
+    quint32 dynamicTableCapacity() const;
+    quint32 maxDynamicTableCapacity() const;
 
     bool encodeRequest(class BitOStream &outputStream,
                        const HttpHeader &header);
@@ -93,6 +95,8 @@ public:
     }
 
     quint32 dynamicTableSize() const;
+    quint32 dynamicTableCapacity() const;
+    quint32 maxDynamicTableCapacity() const;
 
     void setMaxDynamicTableSize(quint32 size);
 
diff --git a/src/network/access/http2/hpacktable.cpp b/src/network/access/http2/hpacktable.cpp
index e06da4e7ddb..73f63b722d4 100644
--- a/src/network/access/http2/hpacktable.cpp
+++ b/src/network/access/http2/hpacktable.cpp
@@ -208,6 +208,16 @@ quint32 FieldLookupTable::dynamicDataSize() const
     return dataSize;
 }
 
+quint32 FieldLookupTable::dynamicDataCapacity() const
+{
+    return tableCapacity;
+}
+
+quint32 FieldLookupTable::maxDynamicDataCapacity() const
+{
+    return maxTableSize;
+}
+
 void FieldLookupTable::clearDynamicTable()
 {
     searchIndex.clear();
@@ -386,6 +396,7 @@ bool FieldLookupTable::updateDynamicTableSize(quint32 size)
 {
     if (!size) {
         clearDynamicTable();
+        tableCapacity = 0;
         return true;
     }
 
@@ -404,10 +415,10 @@ void FieldLookupTable::setMaxDynamicTableSize(quint32 size)
     // This is for an external user, for example, HTTP2 protocol
     // layer that can receive SETTINGS frame from its peer.
     // No validity checks here, up to this external user.
-    // We update max size and capacity (this can also result in
-    // items evicted or even dynamic table completely cleared).
+    // We update max size only, the capacity will be updated
+    // later through the Dynamic Table Size Update mechanism
+    // in HPack.
     maxTableSize = size;
-    updateDynamicTableSize(size);
 }
 
 // This data is from the HPACK's specs and it's quite conveniently sorted,
diff --git a/src/network/access/http2/hpacktable_p.h b/src/network/access/http2/hpacktable_p.h
index 320ba133362..4c91aa3fe20 100644
--- a/src/network/access/http2/hpacktable_p.h
+++ b/src/network/access/http2/hpacktable_p.h
@@ -124,6 +124,8 @@ public:
     quint32 numberOfStaticEntries() const;
     quint32 numberOfDynamicEntries() const;
     quint32 dynamicDataSize() const;
+    quint32 dynamicDataCapacity() const;
+    quint32 maxDynamicDataCapacity() const;
     void clearDynamicTable();
 
     bool indexIsValid(quint32 index) const;
diff --git a/tests/auto/network/access/hpack/tst_hpack.cpp b/tests/auto/network/access/hpack/tst_hpack.cpp
index e6b43eaed45..0092d586803 100644
--- a/tests/auto/network/access/hpack/tst_hpack.cpp
+++ b/tests/auto/network/access/hpack/tst_hpack.cpp
@@ -36,6 +36,8 @@ private Q_SLOTS:
     void lookupTableStatic();
     void lookupTableDynamic();
 
+    void dynamicTableSizeUpdate();
+
     void hpackEncodeRequest_data();
     void hpackEncodeRequest();
     void hpackDecodeRequest_data();
@@ -469,6 +471,30 @@ void tst_Hpack::lookupTableDynamic()
     QVERIFY(table.indexOf("name1") == 0);
 }
 
+void tst_Hpack::dynamicTableSizeUpdate()
+{
+    std::vector<uchar> buffer;
+    buffer.reserve(4096);
+
+    BitOStream out(buffer);
+
+    HPack::Encoder encoder(4096u, true);
+
+    QVERIFY(encoder.encodeSizeUpdate(out, 2048u));
+    QVERIFY(encoder.encodeRequest(out, {{":method", "GET"}, {":path", "/"}, {":scheme", "https"}}));
+
+    BitIStream in(buffer.data(), buffer.data() + buffer.size());
+    HPack::Decoder decoder(4096u);
+    QCOMPARE(decoder.dynamicTableCapacity(), 4096u);
+    QCOMPARE(decoder.maxDynamicTableCapacity(), 4096u);
+
+    QVERIFY(decoder.decodeHeaderFields(in));
+    QCOMPARE(decoder.dynamicTableCapacity(), 2048u);
+    // The max is adjusted out-of-band, so it's not changed here:
+    QCOMPARE(decoder.maxDynamicTableCapacity(), 4096u);
+}
+
+
 void  tst_Hpack::hpackEncodeRequest_data()
 {
     QTest::addColumn<bool>("compression");