diff --git a/SConstruct b/SConstruct
index 1940edba81..0783a4ee65 100644
--- a/SConstruct
+++ b/SConstruct
@@ -1699,6 +1699,8 @@ env["python_max_version"] = python_max_version
 env["py_requires_ver_str"] = py_requires_ver_str
 env["cython_version_spec"] = SpecifierSet(">=0.29.31")
 env["numpy_version_spec"] = SpecifierSet(">=1.12.0,<3")
+env["cython_version_spec_str"] = str(env["cython_version_spec"])
+env["numpy_version_spec_str"] = str(env["numpy_version_spec"])
 
 # We choose ruamel.yaml 0.15.34 as the minimum version
 # since it is the highest version available in the Ubuntu
@@ -1706,6 +1708,7 @@ env["numpy_version_spec"] = SpecifierSet(">=1.12.0,<3")
 # 0.13.14 on CentOS7 and 0.10.23 on Ubuntu 16.04 raise an exception
 # that they are missing the RoundTripRepresenter
 env["ruamel_version_spec"] = SpecifierSet(">=0.15.34")
+env["ruamel_version_spec_str"] = str(env["ruamel_version_spec"])
 
 # Minimum pytest version assumed based on Ubuntu 20.04
 env["pytest_version_spec"] = SpecifierSet(">=4.6.9")
diff --git a/interfaces/cython/setup.cfg.in b/interfaces/cython/setup.cfg.in
index 8c677d87cc..e530871f5c 100644
--- a/interfaces/cython/setup.cfg.in
+++ b/interfaces/cython/setup.cfg.in
@@ -40,9 +40,9 @@ project_urls =
 [options]
 zip_safe = False
 install_requires =
-    numpy @numpy_version_spec!s@
-    ruamel.yaml @ruamel_version_spec!s@
-python_requires @py_requires_ver_str@
+    numpy @numpy_version_spec_str@
+    ruamel.yaml @ruamel_version_spec_str@
+python_requires = @py_requires_ver_str@
 packages =
     cantera
     cantera.data