diff --git a/lib/mathlib.h b/lib/mathlib.h
index 8d4b44bd4..017fc46d0 100644
--- a/lib/mathlib.h
+++ b/lib/mathlib.h
@@ -20,7 +20,7 @@
 #ifndef mathlibH
 #define mathlibH
 
-#include "token.h"
+#include <string>
 
 /// @addtogroup Core
 /// @{
diff --git a/lib/preprocessor.cpp b/lib/preprocessor.cpp
index d1aefd3e2..6aab5bc6a 100644
--- a/lib/preprocessor.cpp
+++ b/lib/preprocessor.cpp
@@ -22,6 +22,7 @@
 #include "token.h"
 #include "filelister.h"
 #include "path.h"
+#include "errorlogger.h"
 
 #include <algorithm>
 #include <stdexcept>
diff --git a/lib/preprocessor.h b/lib/preprocessor.h
index e502794de..ffc36410c 100644
--- a/lib/preprocessor.h
+++ b/lib/preprocessor.h
@@ -25,8 +25,9 @@
 #include <istream>
 #include <string>
 #include <list>
-#include "errorlogger.h"
-#include "settings.h"
+
+class ErrorLogger;
+class Settings;
 
 /// @addtogroup Core
 /// @{
diff --git a/lib/tokenize.cpp b/lib/tokenize.cpp
index e477d4bd2..262afb21e 100644
--- a/lib/tokenize.cpp
+++ b/lib/tokenize.cpp
@@ -29,6 +29,7 @@
 #include "settings.h"
 #include "errorlogger.h"
 #include "check.h"
+#include "classinfo.h"
 
 #include <locale>
 #include <fstream>
diff --git a/lib/tokenize.h b/lib/tokenize.h
index 46439a790..1c0d47716 100644
--- a/lib/tokenize.h
+++ b/lib/tokenize.h
@@ -25,8 +25,8 @@
 #include <string>
 #include <map>
 #include <vector>
-#include "classinfo.h"
 
+class ClassInfo;
 class Token;
 class ErrorLogger;
 class Settings;
diff --git a/test/testtokenize.cpp b/test/testtokenize.cpp
index 9e5b5eed1..2557e418d 100644
--- a/test/testtokenize.cpp
+++ b/test/testtokenize.cpp
@@ -25,6 +25,7 @@
 #include "testsuite.h"
 #include "tokenize.h"
 #include "token.h"
+#include "classinfo.h"
 
 extern std::ostringstream errout;
 class TestTokenizer : public TestFixture