diff --git a/data/CMakeLists.txt b/data/CMakeLists.txt
--- a/data/CMakeLists.txt
+++ b/data/CMakeLists.txt
@@ -12,12 +12,16 @@
 
 # find all definitions
 file(GLOB src_defs "${CMAKE_CURRENT_SOURCE_DIR}/syntax/*.xml")
-set(defs
-    ${src_defs}
-    ${CMAKE_CURRENT_BINARY_DIR}/syntax/html-php.xml
-    ${CMAKE_CURRENT_BINARY_DIR}/syntax/css-php.xml
-    ${CMAKE_CURRENT_BINARY_DIR}/syntax/javascript-php.xml
-)
+if(CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_CURRENT_BINARY_DIR)
+    set(defs ${src_defs})
+else()
+    set(defs
+        ${src_defs}
+        ${CMAKE_CURRENT_BINARY_DIR}/syntax/html-php.xml
+        ${CMAKE_CURRENT_BINARY_DIR}/syntax/css-php.xml
+        ${CMAKE_CURRENT_BINARY_DIR}/syntax/javascript-php.xml
+    )
+endif()
 
 # theme data resource
 qt5_add_resources(themes_QRC ${CMAKE_CURRENT_SOURCE_DIR}/themes/theme-data.qrc)