diff --git a/cmake/tool.tmpl b/cmake/tool.tmpl
index 3bba72c3..c73249b1 100755
--- a/cmake/tool.tmpl
+++ b/cmake/tool.tmpl
@@ -4,7 +4,7 @@ import os
 
 sys.path.insert(1, '@CMAKE_SOURCE_DIR@')
 
-os.environ['NOMINATIM_NOMINATIM_TOOL'] = __file__
+os.environ['NOMINATIM_NOMINATIM_TOOL'] = os.path.abspath(__file__)
 
 from nominatim import cli