diff --git a/external/fastjet/CMakeLists.txt b/external/fastjet/CMakeLists.txt
index a10c289..199e43c 100644
--- a/external/fastjet/CMakeLists.txt
+++ b/external/fastjet/CMakeLists.txt
@@ -56,7 +56,7 @@ message(STATUS "FASTJET_HEPPY_PREFIX ${FASTJET_HEPPY_PREFIX}")
 find_package(Python 3.6 REQUIRED COMPONENTS Interpreter Development NumPy)
 set($ENV{PYTHON} ${Python3_EXECUTABLE})
 message(STATUS "Python version string is ${Python_VERSION}")
-string(REGEX MATCHALL "[0-9]" PYTHON_VER_MATCH "${Python_VERSION}")
+string(REGEX MATCHALL "[0-9]+" PYTHON_VER_MATCH "${Python_VERSION}")
 list(GET PYTHON_VER_MATCH 0 Python_Ver_Major)
 list(GET PYTHON_VER_MATCH 1 Python_Ver_Minor)
 list(GET PYTHON_VER_MATCH 2 Python_Ver_Patch)