diff --git a/interfaces/python_minimal/SConscript b/interfaces/python_minimal/SConscript
index c764bd3645..1ae8a19370 100644
--- a/interfaces/python_minimal/SConscript
+++ b/interfaces/python_minimal/SConscript
@@ -32,7 +32,6 @@ localenv.Depends(mod, [make_setup, readme, license, "setup.py", "pyproject.toml"
 install_cmd = ["$python_cmd_esc", "-m", "pip", "install"]
 user_install = False
 python_prefix = None
-python_root = None
 if localenv["PYTHON_INSTALLER"] == "direct":
     if localenv["python_prefix"] == "USER":
         # Install to the OS-dependent user site-packages directory
@@ -40,9 +39,12 @@ if localenv["PYTHON_INSTALLER"] == "direct":
         user_install = True
     elif localenv["python_prefix"]:
         # A specific location for the Cantera python module has been given
-        install_cmd.extend((f"--prefix={localenv.subst('python_prefix')}",
+        install_cmd.extend((f"--prefix={localenv.subst('$python_prefix')}",
                             "--no-warn-script-location"))
-        python_prefix = localenv.subst("python_prefix")
+        python_prefix = localenv.subst("$python_prefix")
+    elif not env["default_prefix"]:
+        install_cmd.append(f"--prefix={env['prefix']}")
+        python_prefix = env["prefix"]
 
 if env["stage_dir"]:
     # Get the absolute path to the stage directory. If the stage directory is a relative