diff --git a/include/IwyuFilter_include.yaml b/include/IwyuFilter_include.yaml
index 0825eb8faa1a..f3513cba7d5f 100644
--- a/include/IwyuFilter_include.yaml
+++ b/include/IwyuFilter_include.yaml
@@ -262,3 +262,14 @@ blacklist:
     - com/sun/star/io/XOutputStream.hpp
     - com/sun/star/io/XStream.hpp
     - com/sun/star/io/XTruncate.hpp
+    include/sax/fshelper.hxx:
+    # base class has to be a complete type
+    - com/sun/star/xml/sax/XFastAttributeList.hpp
+    include/sax/fastattribs.hxx:
+    # base class has to be a complete type
+    - com/sun/star/xml/sax/XFastAttributeList.hpp
+    include/sax/fastparser.hxx:
+    # base class has to be a complete type
+    - com/sun/star/lang/XInitialization.hpp
+    - com/sun/star/lang/XServiceInfo.hpp
+    - com/sun/star/xml/sax/XFastParser.hpp
diff --git a/include/sax/fastattribs.hxx b/include/sax/fastattribs.hxx
index a0f552226fe6..f8005a65a27a 100644
--- a/include/sax/fastattribs.hxx
+++ b/include/sax/fastattribs.hxx
@@ -21,16 +21,16 @@
 #define INCLUDED_SAX_FASTATTRIBS_HXX
 
 #include <com/sun/star/xml/sax/XFastAttributeList.hpp>
-#include <com/sun/star/xml/sax/XFastTokenHandler.hpp>
-#include <com/sun/star/xml/Attribute.hpp>
-#include <com/sun/star/xml/FastAttribute.hpp>
 
 #include <cppuhelper/implbase.hxx>
 #include <sax/saxdllapi.h>
 
-#include <map>
 #include <vector>
 
+namespace com { namespace sun { namespace star { namespace xml { namespace sax { class XFastTokenHandler; } } } } }
+namespace com { namespace sun { namespace star { namespace xml { struct Attribute; } } } }
+namespace com { namespace sun { namespace star { namespace xml { struct FastAttribute; } } } }
+
 namespace sax_fastparser
 {
 
diff --git a/include/sax/fastparser.hxx b/include/sax/fastparser.hxx
index cb82dcf17210..ace7956382fb 100644
--- a/include/sax/fastparser.hxx
+++ b/include/sax/fastparser.hxx
@@ -22,7 +22,6 @@
 
 #include <com/sun/star/xml/sax/XFastParser.hpp>
 #include <com/sun/star/lang/XServiceInfo.hpp>
-#include <cppuhelper/weak.hxx>
 #include <cppuhelper/implbase.hxx>
 #include <com/sun/star/lang/XInitialization.hpp>
 
@@ -31,7 +30,6 @@
 
 namespace com { namespace sun { namespace star { namespace xml { namespace sax {
 
-class XFastContextHandler;
 class XFastDocumentHandler;
 class XFastTokenHandler;
 
diff --git a/include/sax/fshelper.hxx b/include/sax/fshelper.hxx
index 70ef1025218b..159b834a2fe1 100644
--- a/include/sax/fshelper.hxx
+++ b/include/sax/fshelper.hxx
@@ -20,12 +20,16 @@
 #ifndef INCLUDED_SAX_FSHELPER_HXX
 #define INCLUDED_SAX_FSHELPER_HXX
 
-#include <com/sun/star/io/XOutputStream.hpp>
-#include <sax/fastattribs.hxx>
-#include <stdarg.h>
+#include <com/sun/star/xml/sax/XFastAttributeList.hpp>
+#include <com/sun/star/uno/Reference.hxx>
+#include <com/sun/star/uno/Sequence.hxx>
+#include <sax/saxdllapi.h>
 #include <memory>
 #include <utility>
 
+namespace com { namespace sun { namespace star { namespace io { class XOutputStream; } } } }
+namespace sax_fastparser { class FastAttributeList; }
+
 #define FSNS(namespc, element) ((namespc << 16) | element)
 // Backwards compatibility for code that used FSEND to terminate the vararg.
 // As soon as no supported LO version has the varargs code, this can be removed entirely
diff --git a/include/sax/tools/converter.hxx b/include/sax/tools/converter.hxx
index a8880d962920..d1dbdac62d54 100644
--- a/include/sax/tools/converter.hxx
+++ b/include/sax/tools/converter.hxx
@@ -25,7 +25,6 @@
 #include <sal/types.h>
 #include <rtl/ustring.hxx>
 #include <rtl/ustrbuf.hxx>
-#include <com/sun/star/uno/Sequence.h>
 #include <com/sun/star/util/MeasureUnit.hpp>
 #include <tools/color.hxx>
 
@@ -38,8 +37,6 @@ namespace com { namespace sun { namespace star {
     namespace util {
         struct Date;
         struct DateTime;
-        struct DateWithTimezone;
-        struct DateTimeWithTimezone;
         struct Duration;
     }
 } } }
diff --git a/include/sax/tools/documenthandleradapter.hxx b/include/sax/tools/documenthandleradapter.hxx
index 4e2a1c17738a..202bfbcb42a2 100644
--- a/include/sax/tools/documenthandleradapter.hxx
+++ b/include/sax/tools/documenthandleradapter.hxx
@@ -11,7 +11,6 @@
 #ifndef INCLUDED_SAX_TOOLS_DOCUMENTHANDLERADAPTER_HXX
 #define INCLUDED_SAX_TOOLS_DOCUMENTHANDLERADAPTER_HXX
 
-#include <com/sun/star/xml/sax/SAXException.hpp>
 #include <com/sun/star/xml/sax/XDocumentHandler.hpp>
 #include <com/sun/star/xml/sax/XExtendedDocumentHandler.hpp>
 
diff --git a/oox/source/export/drawingml.cxx b/oox/source/export/drawingml.cxx
index 5968cd9dd67c..573d2982cc88 100644
--- a/oox/source/export/drawingml.cxx
+++ b/oox/source/export/drawingml.cxx
@@ -33,6 +33,7 @@
 #include <oox/token/tokens.hxx>
 #include <oox/drawingml/drawingmltypes.hxx>
 #include <svtools/unitconv.hxx>
+#include <sax/fastattribs.hxx>
 
 #include <cstdio>
 #include <com/sun/star/awt/CharSet.hpp>
diff --git a/oox/source/export/vmlexport.cxx b/oox/source/export/vmlexport.cxx
index 0ec745e69d45..ff3631236868 100644
--- a/oox/source/export/vmlexport.cxx
+++ b/oox/source/export/vmlexport.cxx
@@ -22,6 +22,7 @@
 #include <svl/itemset.hxx>
 #include <oox/export/drawingml.hxx>
 #include <oox/export/vmlexport.hxx>
+#include <sax/fastattribs.hxx>
 
 #include <oox/token/tokens.hxx>
 
diff --git a/sax/source/tools/fastattribs.cxx b/sax/source/tools/fastattribs.cxx
index d7ecbc1bd13d..21d36d30b81c 100644
--- a/sax/source/tools/fastattribs.cxx
+++ b/sax/source/tools/fastattribs.cxx
@@ -20,6 +20,7 @@
 #include <algorithm>
 
 #include <com/sun/star/xml/sax/SAXException.hpp>
+#include <com/sun/star/xml/sax/XFastTokenHandler.hpp>
 #include <sax/fastattribs.hxx>
 
 using namespace ::com::sun::star::uno;
diff --git a/sc/source/filter/excel/xepage.cxx b/sc/source/filter/excel/xepage.cxx
index a039e40fb2bf..fc5828ef3040 100644
--- a/sc/source/filter/excel/xepage.cxx
+++ b/sc/source/filter/excel/xepage.cxx
@@ -29,6 +29,7 @@
 #include <editeng/brushitem.hxx>
 #include <oox/export/utils.hxx>
 #include <oox/token/tokens.hxx>
+#include <sax/fastattribs.hxx>
 #include <document.hxx>
 #include <stlpool.hxx>
 #include <stlsheet.hxx>
diff --git a/sc/source/filter/excel/xepivotxml.cxx b/sc/source/filter/excel/xepivotxml.cxx
index bb2dc847d75f..753746bb8f74 100644
--- a/sc/source/filter/excel/xepivotxml.cxx
+++ b/sc/source/filter/excel/xepivotxml.cxx
@@ -20,6 +20,7 @@
 #include <oox/export/utils.hxx>
 #include <oox/token/namespaces.hxx>
 #include <sax/tools/converter.hxx>
+#include <sax/fastattribs.hxx>
 
 #include <com/sun/star/sheet/DataPilotFieldOrientation.hpp>
 #include <com/sun/star/sheet/DataPilotFieldLayoutMode.hpp>
diff --git a/sw/source/filter/ww8/docxattributeoutput.cxx b/sw/source/filter/ww8/docxattributeoutput.cxx
index fb94a73eaa4e..1681f03e629d 100644
--- a/sw/source/filter/ww8/docxattributeoutput.cxx
+++ b/sw/source/filter/ww8/docxattributeoutput.cxx
@@ -145,6 +145,7 @@
 #include <com/sun/star/embed/EmbedStates.hpp>
 
 #include <algorithm>
+#include <stdarg.h>
 
 using ::editeng::SvxBorderLine;
 
diff --git a/sw/source/filter/ww8/docxtablestyleexport.cxx b/sw/source/filter/ww8/docxtablestyleexport.cxx
index e6a2ebee8316..6b405f3d4a2f 100644
--- a/sw/source/filter/ww8/docxtablestyleexport.cxx
+++ b/sw/source/filter/ww8/docxtablestyleexport.cxx
@@ -14,6 +14,7 @@
 #include <oox/token/tokens.hxx>
 #include <comphelper/sequenceashashmap.hxx>
 #include <o3tl/make_unique.hxx>
+#include <sax/fastattribs.hxx>
 
 #include <boost/optional.hpp>
 
diff --git a/unoxml/source/dom/document.hxx b/unoxml/source/dom/document.hxx
index 1211e5978ea9..8666d2185f0d 100644
--- a/unoxml/source/dom/document.hxx
+++ b/unoxml/source/dom/document.hxx
@@ -22,6 +22,7 @@
 
 #include <set>
 #include <memory>
+#include <map>
 
 #include <libxml/tree.h>