diff --git a/targets/mbedos5/tools/requirements.txt b/targets/mbedos5/tools/requirements.txt
index 54b167dc1..8a5573694 100644
--- a/targets/mbedos5/tools/requirements.txt
+++ b/targets/mbedos5/tools/requirements.txt
@@ -1,3 +1,3 @@
-pycparser
+pycparser<=2.17 # generate_pins.py does not work with 2.18 version
 simpleeval
 pycparserext