diff --git a/CMakeLists.txt b/CMakeLists.txt
index af3665e3..61346040 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -46,14 +46,8 @@ set (${project}_DEPS
 	"dune-istl"
 	)
 
-# C++ project
-cmake_minimum_required (VERSION 2.8)
-project (${${project}_NAME})
-enable_language (C)
-enable_language (CXX)
-
 # additional search modules
-set (${project}_MODULE_DIR "${PROJECT_SOURCE_DIR}/cmake/Modules")
+set (${project}_MODULE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules")
 list (APPEND CMAKE_MODULE_PATH ${${project}_MODULE_DIR})
 
 # include special
@@ -67,6 +61,16 @@ if (CMAKE_VERSION VERSION_LESS "2.8.7")
 	list (APPEND CMAKE_MODULE_PATH "${${project}_MODULE_DIR}/compat-2.8.7")
 endif (CMAKE_VERSION VERSION_LESS "2.8.7")
 
+# don't write default flags into the cache, preserve that for user set values
+include (AddOptions)
+no_default_options ()
+
+# C++ project
+cmake_minimum_required (VERSION 2.8)
+project (${${project}_NAME})
+enable_language (C)
+enable_language (CXX)
+
 # print system information to better pinpoint issues from log alone
 include (UseSystemInfo)
 system_info ()
diff --git a/cmake/Modules/AddOptions.cmake b/cmake/Modules/AddOptions.cmake
index a5fb3864..0ebb8236 100644
--- a/cmake/Modules/AddOptions.cmake
+++ b/cmake/Modules/AddOptions.cmake
@@ -59,3 +59,24 @@ function (add_options langs builds)
 	endforeach (build)
   endforeach (lang)
 endfunction (add_options lang build)
+
+# set varname to flag unless user has specified something that matches regex
+function (set_default_option varname flag regex)
+  if (NOT "$ENV{CXXFLAGS}" MATCHES "${regex}"
+	  AND NOT "${CMAKE_CXX_FLAGS}" MATCHES "${regex}"
+	  AND NOT "${CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE}}" MATCHES "${regex}")
+	set (${varname} ${flag} PARENT_SCOPE)
+  else (NOT "$ENV{CXXFLAGS}" MATCHES "${regex}"
+	  AND NOT "${CMAKE_CXX_FLAGS}" MATCHES "${regex}"
+	  AND NOT "${CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE}}" MATCHES "${regex}")
+	set (${varname} PARENT_SCOPE)
+  endif (NOT "$ENV{CXXFLAGS}" MATCHES "${regex}"
+	AND NOT "${CMAKE_CXX_FLAGS}" MATCHES "${regex}"
+	AND NOT "${CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE}}" MATCHES "${regex}")
+endfunction (set_default_option)
+
+# note: this must be called before project()
+macro (no_default_options)
+  # prevent the platform probe to set options
+  set (CMAKE_NOT_USING_CONFIG_FLAGS TRUE)
+endmacro (no_default_options)
diff --git a/cmake/Modules/UseDebugSymbols.cmake b/cmake/Modules/UseDebugSymbols.cmake
index 175579c1..10ec7e83 100644
--- a/cmake/Modules/UseDebugSymbols.cmake
+++ b/cmake/Modules/UseDebugSymbols.cmake
@@ -13,11 +13,16 @@ include (AddOptions)
 
 # only debugging using the GNU toolchain is supported for now
 if (CMAKE_COMPILER_IS_GNUCXX)
+  # default debug level, if not specified by the user
+  set_default_option (_dbg_flag "-ggdb3" "(^|\ )-g")
+
   # add debug symbols to *all* targets, regardless. there WILL come a
   # time when you need to find a bug which only manifests itself in a
   # release target on a production system!
-  message (STATUS "Generating debug symbols: -ggdb3")
-  add_options (ALL_LANGUAGES ALL_BUILDS "-ggdb3")
+  if (_dbg_flag)
+	message (STATUS "Generating debug symbols: ${_dbg_flag}")
+	add_options (ALL_LANGUAGES ALL_BUILDS "${_dbg_flag}")
+  endif (_dbg_flag)
 
   # extracting the debug info is done by a separate utility in the GNU
   # toolchain. check that this is actually installed.
diff --git a/cmake/Modules/UseOptimization.cmake b/cmake/Modules/UseOptimization.cmake
index e66f7a22..1a196355 100644
--- a/cmake/Modules/UseOptimization.cmake
+++ b/cmake/Modules/UseOptimization.cmake
@@ -7,11 +7,15 @@ include (AddOptions)
 # otherwise, turn them on. indicate to the code what we have done
 # so it can turn on assertions etc.
 if (CMAKE_COMPILER_IS_GNUCXX)
+  # default optimization flags, if not set by user
+  set_default_option (_opt_dbg "-O0" "(^|\ )-O")
+  set_default_option (_opt_rel "-O3" "(^|\ )-O")
+
   # use these options for debug builds - no optimizations
   add_options (
 	ALL_LANGUAGES
 	"Debug"
-	"-O0" "-DDEBUG"
+	${_opt_dbg} "-DDEBUG"
 	)
 
   # extra flags passed for optimization
@@ -36,6 +40,25 @@ if (CMAKE_COMPILER_IS_GNUCXX)
   add_options (
 	ALL_LANGUAGES
 	"Release;RelWithDebInfo;MinSizeRel"
-	"-O3" "-DNDEBUG" ${_opt_flags}
+	${_opt_rel} "-DNDEBUG" ${_opt_flags}
 	)
+else (CMAKE_COMPILER_IS_GNUCXX)
+  # mapping from profile name (in CMAKE_BUILD_TYPE) to variable part
+  set (_prof_DEBUG "Debug")
+  set (_prof_RELEASE "Release;RelWithDebInfo;MinSizeRel")
+  
+  # default information from system
+  foreach (lang IN ITEMS C CXX Fortran)
+	if (lang STREQUAL "Fortran")
+	  set (_lang F)
+	else (lang STREQUAL "Fortran")
+	  set (_lang ${lang})
+	endif (lang STREQUAL "Fortran")
+	foreach (profile IN ITEMS DEBUG RELEASE)
+	  if (NOT CMAKE_${lang}_FLAGS_${profile})
+		add_options (${lang} "${_prof_${profile}}"
+		  "$ENV{${_lang}FLAGS} ${CMAKE_${lang}_FLAGS_${profile}_INIT}")
+	  endif (NOT CMAKE_${lang}_FLAGS_${profile})
+	endforeach (profile)
+  endforeach (lang)
 endif (CMAKE_COMPILER_IS_GNUCXX)
diff --git a/cmake/Modules/UseWarnings.cmake b/cmake/Modules/UseWarnings.cmake
index 2dce6453..65e8dcc6 100644
--- a/cmake/Modules/UseWarnings.cmake
+++ b/cmake/Modules/UseWarnings.cmake
@@ -2,6 +2,10 @@
 
 include (AddOptions)
 if (CMAKE_COMPILER_IS_GNUCXX)
-  message (STATUS "All warnings enabled: -Wall")
-  add_options (ALL_LANGUAGES ALL_BUILDS "-Wall")
+  # default warnings flags, if not set by user
+  set_default_option (_warn_flag "-Wall" "(^|\ )-W")
+  if (_warn_flag)
+	message (STATUS "All warnings enabled: ${_warn_flag}")
+	add_options (ALL_LANGUAGES ALL_BUILDS "${_warn_flag}")
+  endif (_warn_flag)
 endif (CMAKE_COMPILER_IS_GNUCXX)