diff --git a/CMakeLists.txt b/CMakeLists.txt
index 79c666483..9f3cf19ba 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,8 +3,14 @@ PROJECT( Assimp )
 
 INCLUDE_DIRECTORIES( include )
 
-SET( CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_HOME_DIRECTORY}/lib )
-SET( CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_HOME_DIRECTORY}/bin ) 
+# If this is an in-source build (CMAKE_SOURCE_DIR == CMAKE_BINARY_DIR),
+# write the library/executable files to the respective directories in the
+# source tree. During an out-of-source build, however, do not litter this
+# directory, since that is probably what the user wanted to avoid.
+IF ( CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR )
+	SET( CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_HOME_DIRECTORY}/lib )
+	SET( CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_HOME_DIRECTORY}/bin )
+ENDIF ( CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR )
 
 # Cache these to allow the user to override them manually.
 SET( LIB_INSTALL_DIR "${CMAKE_INSTALL_PREFIX}/lib" CACHE PATH