diff --git a/doc/sphinx/conf.py b/doc/sphinx/conf.py
index 34a15e9..86d6222 100644
--- a/doc/sphinx/conf.py
+++ b/doc/sphinx/conf.py
@@ -5,7 +5,7 @@ read_the_docs_build = os.environ.get('READTHEDOCS', None) == 'True'
 breathe_projects = {}
 
 if read_the_docs_build:
-	subprocess.call('cd /usr/share/plantuml; sudo rm plantuml.jar; wget sudo wget https://sourceforge.net/projects/plantuml/files/plantuml.jar')
+	subprocess.call('cd /usr/share/plantuml; sudo rm plantuml.jar; wget sudo wget https://sourceforge.net/projects/plantuml/files/plantuml.jar', shell=True)
 	subprocess.call('cd .. ; doxygen', shell=True)
 	breathe_projects['knx'] = '../build/xml'
 	html_extra_path = ['../build/html']