diff --git a/Tools/environment_install/install-prereqs-ubuntu.sh b/Tools/environment_install/install-prereqs-ubuntu.sh
index 2a125faa42..0f27d11bdf 100755
--- a/Tools/environment_install/install-prereqs-ubuntu.sh
+++ b/Tools/environment_install/install-prereqs-ubuntu.sh
@@ -164,8 +164,8 @@ else
 fi
 
 # Lists of packages to install
-BASE_PKGS="build-essential ccache g++ gawk git make wget valgrind screen"
-PYTHON_PKGS="future lxml pymavlink pyserial MAVProxy pexpect geocoder empy==3.3.4 ptyprocess dronecan"
+BASE_PKGS="build-essential ccache g++ gawk git make wget valgrind screen python3-pexpect"
+PYTHON_PKGS="future lxml pymavlink pyserial MAVProxy geocoder empy==3.3.4 ptyprocess dronecan"
 PYTHON_PKGS="$PYTHON_PKGS flake8 junitparser"
 
 # add some Python packages required for commonly-used MAVProxy modules and hex file generation: