Add operator and quotes to the AX_PYTHON_DEVEL parameter The operator is required and the quotes are needed to protect PYTHON_VERSION. See-also: https://www.gnu.org/software/autoconf-archive/ax_python_devel.html Fixes: checking whether to build the libpst python interface... yes checking for python build information... checking for python3.7... python3.7 checking for main in -lpython3.7... no checking for main in -lpython3.7m... yes results of the Python check: Binary: python3.7 Library: python3.7m Include Dir: /usr/include/python3.7m checking for python3.7... /usr/bin/python3.7 checking for a version of Python >= '2.1.0'... yes checking for a version of Python 3.7... File "<string>", line 1 import sys; ver = sys.version.split ()[0]; print (ver 3.7) ^ SyntaxError: invalid syntax no configure: error: this package requires Python 3.7. If you have it installed, but it isn't the default Python interpreter in your system path, please pass the PYTHON_VERSION variable to configure. See ``configure --help'' for reference.