diff --git a/gcc/diagnostics/buffering.cc b/gcc/diagnostics/buffering.cc
index b09d1c2cc157..019c9927c6d2 100644
--- a/gcc/diagnostics/buffering.cc
+++ b/gcc/diagnostics/buffering.cc
@@ -21,7 +21,6 @@ along with GCC; see the file COPYING3.  If not see
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
-#include "diagnostic.h"
 #include "diagnostics/buffering.h"
 #include "diagnostics/sink.h"
 #include "diagnostics/dumping.h"
diff --git a/gcc/diagnostics/buffering.h b/gcc/diagnostics/buffering.h
index 9b86fee90fe8..24a57e4a5f9a 100644
--- a/gcc/diagnostics/buffering.h
+++ b/gcc/diagnostics/buffering.h
@@ -21,7 +21,7 @@ along with GCC; see the file COPYING3.  If not see
 #ifndef GCC_DIAGNOSTICS_BUFFERING_H
 #define GCC_DIAGNOSTICS_BUFFERING_H
 
-#include "diagnostic.h"
+#include "diagnostics/counters.h"
 
 namespace diagnostics {
 
diff --git a/gcc/diagnostics/context.h b/gcc/diagnostics/context.h
index 9464f6adb6c9..7d7c87250be2 100644
--- a/gcc/diagnostics/context.h
+++ b/gcc/diagnostics/context.h
@@ -47,6 +47,7 @@ namespace diagnostics {
   class diagram;
   class sink;
     class text_sink;
+  class metadata;
 
   class source_effect_info;
 
diff --git a/gcc/diagnostics/html-sink.cc b/gcc/diagnostics/html-sink.cc
index 64dcefeedaad..d3fb107e6145 100644
--- a/gcc/diagnostics/html-sink.cc
+++ b/gcc/diagnostics/html-sink.cc
@@ -24,7 +24,6 @@ along with GCC; see the file COPYING3.  If not see
 #define INCLUDE_VECTOR
 #include "system.h"
 #include "coretypes.h"
-#include "diagnostic.h"
 #include "diagnostics/metadata.h"
 #include "diagnostics/sink.h"
 #include "diagnostics/html-sink.h"
diff --git a/gcc/diagnostics/lazy-paths.cc b/gcc/diagnostics/lazy-paths.cc
index f246eea94205..d25f8fb37814 100644
--- a/gcc/diagnostics/lazy-paths.cc
+++ b/gcc/diagnostics/lazy-paths.cc
@@ -23,7 +23,6 @@ along with GCC; see the file COPYING3.  If not see
 #define INCLUDE_VECTOR
 #include "system.h"
 #include "coretypes.h"
-#include "diagnostic.h"
 #include "diagnostics/lazy-paths.h"
 #include "selftest.h"
 #include "diagnostics/selftest-context.h"
diff --git a/gcc/diagnostics/macro-unwinding.cc b/gcc/diagnostics/macro-unwinding.cc
index 66bad1c32a75..fb4ee65f4244 100644
--- a/gcc/diagnostics/macro-unwinding.cc
+++ b/gcc/diagnostics/macro-unwinding.cc
@@ -21,7 +21,6 @@ along with GCC; see the file COPYING3.  If not see
 #include "system.h"
 #include "coretypes.h"
 #include "tree.h"
-#include "diagnostic.h"
 #include "diagnostics/macro-unwinding.h"
 #include "diagnostics/text-sink.h"
 #include "intl.h"
diff --git a/gcc/diagnostics/macro-unwinding.h b/gcc/diagnostics/macro-unwinding.h
index 1f28d584c258..1df8715e2bd9 100644
--- a/gcc/diagnostics/macro-unwinding.h
+++ b/gcc/diagnostics/macro-unwinding.h
@@ -22,6 +22,8 @@ along with GCC; see the file COPYING3.  If not see
 
 namespace diagnostics {
 
+struct diagnostic_info;
+
 extern void virt_loc_aware_text_finalizer (text_sink &,
 					   const diagnostic_info *);
 
diff --git a/gcc/diagnostics/option-classifier.h b/gcc/diagnostics/option-classifier.h
index 3b16c740b7ea..9457fe8d1335 100644
--- a/gcc/diagnostics/option-classifier.h
+++ b/gcc/diagnostics/option-classifier.h
@@ -20,10 +20,14 @@ along with GCC; see the file COPYING3.  If not see
 #ifndef GCC_DIAGNOSTICS_OPTION_CLASSIFIER_H
 #define GCC_DIAGNOSTICS_OPTION_CLASSIFIER_H
 
+#include "diagnostics/option-id.h"
+#include "diagnostics/kinds.h"
+
 namespace diagnostics {
 
 /*  Forward declarations.  */
 class context;
+struct diagnostic_info;
 
 /* A stack of sets of classifications: each entry in the stack is
    a mapping from option index to diagnostic severity that can be changed
diff --git a/gcc/diagnostics/output-spec.cc b/gcc/diagnostics/output-spec.cc
index e25d25a9a9a4..8ec638a83bf1 100644
--- a/gcc/diagnostics/output-spec.cc
+++ b/gcc/diagnostics/output-spec.cc
@@ -31,7 +31,6 @@ along with GCC; see the file COPYING3.  If not see
 #include "coretypes.h"
 #include "version.h"
 #include "intl.h"
-#include "diagnostic.h"
 #include "diagnostics/color.h"
 #include "diagnostics/sink.h"
 #include "diagnostics/html-sink.h"
diff --git a/gcc/diagnostics/paths-output.cc b/gcc/diagnostics/paths-output.cc
index a3ac9a0519ac..2c97bf40679e 100644
--- a/gcc/diagnostics/paths-output.cc
+++ b/gcc/diagnostics/paths-output.cc
@@ -25,7 +25,6 @@ along with GCC; see the file COPYING3.  If not see
 #define INCLUDE_VECTOR
 #include "system.h"
 #include "coretypes.h"
-#include "diagnostic.h"
 #include "diagnostics/macro-unwinding.h"
 #include "intl.h"
 #include "diagnostics/paths.h"
diff --git a/gcc/diagnostics/paths.cc b/gcc/diagnostics/paths.cc
index bc769c45766e..824b810cb3bf 100644
--- a/gcc/diagnostics/paths.cc
+++ b/gcc/diagnostics/paths.cc
@@ -25,7 +25,6 @@ along with GCC; see the file COPYING3.  If not see
 #define INCLUDE_VECTOR
 #include "system.h"
 #include "coretypes.h"
-#include "diagnostic.h"
 #include "diagnostics/paths.h"
 #include "diagnostics/state-graphs.h"
 
diff --git a/gcc/diagnostics/sarif-sink.cc b/gcc/diagnostics/sarif-sink.cc
index bc121388bb87..144040e9dfb1 100644
--- a/gcc/diagnostics/sarif-sink.cc
+++ b/gcc/diagnostics/sarif-sink.cc
@@ -26,7 +26,6 @@ along with GCC; see the file COPYING3.  If not see
 #define INCLUDE_VECTOR
 #include "system.h"
 #include "coretypes.h"
-#include "diagnostic.h"
 #include "diagnostics/metadata.h"
 #include "diagnostics/digraphs.h"
 #include "diagnostics/state-graphs.h"
diff --git a/gcc/diagnostics/selftest-context.cc b/gcc/diagnostics/selftest-context.cc
index 2b6dd0b331fb..2eced4d3cd85 100644
--- a/gcc/diagnostics/selftest-context.cc
+++ b/gcc/diagnostics/selftest-context.cc
@@ -20,7 +20,6 @@ along with GCC; see the file COPYING3.  If not see
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
-#include "diagnostic.h"
 #include "diagnostics/sink.h"
 #include "selftest.h"
 #include "diagnostics/selftest-context.h"
diff --git a/gcc/diagnostics/selftest-paths.cc b/gcc/diagnostics/selftest-paths.cc
index 56ce7ffcae14..e28d18a6370f 100644
--- a/gcc/diagnostics/selftest-paths.cc
+++ b/gcc/diagnostics/selftest-paths.cc
@@ -24,7 +24,6 @@ along with GCC; see the file COPYING3.  If not see
 #include "system.h"
 #include "coretypes.h"
 #include "version.h"
-#include "diagnostic.h"
 #include "diagnostics/selftest-paths.h"
 
 #if CHECKING_P
diff --git a/gcc/diagnostics/source-printing-options.h b/gcc/diagnostics/source-printing-options.h
index 362b691c90c6..842a3e77d20c 100644
--- a/gcc/diagnostics/source-printing-options.h
+++ b/gcc/diagnostics/source-printing-options.h
@@ -20,6 +20,8 @@ along with GCC; see the file COPYING3.  If not see
 #ifndef GCC_DIAGNOSTICS_SOURCE_PRINTING_OPTIONS_H
 #define GCC_DIAGNOSTICS_SOURCE_PRINTING_OPTIONS_H
 
+#include "rich-location.h"
+
 namespace diagnostics {
 
 /* A bundle of options relating to printing the user's source code
diff --git a/gcc/diagnostics/text-sink.cc b/gcc/diagnostics/text-sink.cc
index d4cfb89347f4..f9a2bffb2630 100644
--- a/gcc/diagnostics/text-sink.cc
+++ b/gcc/diagnostics/text-sink.cc
@@ -24,7 +24,6 @@ along with GCC; see the file COPYING3.  If not see
 #include "coretypes.h"
 #include "version.h"
 #include "intl.h"
-#include "diagnostic.h"
 #include "diagnostics/color.h"
 #include "diagnostics/url.h"
 #include "diagnostics/metadata.h"