diff --git a/util/check_package_config.py b/util/check_package_config.py
index bd119468c..26e234e2c 100755
--- a/util/check_package_config.py
+++ b/util/check_package_config.py
@@ -11,12 +11,13 @@
 import json
 import os
 import sys
+
 import yaml
 
 SPACK_ENV = os.getenv("SPACK_ENV")
 assert SPACK_ENV, "$SPACK_ENV must be set but is not!"
 
-## Load common/packages.yaml and site/packages.yaml for versions and externals, respectively
+# Load common/packages.yaml and site/packages.yaml for versions and externals, respectively
 packages_versions_path = os.path.join(SPACK_ENV, "common", "packages.yaml")
 with open(packages_versions_path, "r") as f:
     packages_versions = yaml.safe_load(f)
@@ -25,19 +26,19 @@
 with open(packages_externals_path, "r") as f:
     packages_externals = yaml.safe_load(f)
 
-## Load spack.lock
+# Load spack.lock
 spack_lock_path = os.path.join(SPACK_ENV, "spack.lock")
 with open(spack_lock_path, "r") as f:
     spack_lock = json.load(f)
 
 iret = 0
 
-## Iterate over concretized packages
+# Iterate over concretized packages
 for concrete_spec in spack_lock["concrete_specs"].values():
     concrete_name = concrete_spec["name"]
     # Ignore user-specified packages:
     if concrete_name in sys.argv[1:]:
-      continue
+        continue
     concrete_version = concrete_spec["version"]
     if concrete_name in packages_versions["packages"].keys():
         # Check whether concretized package has specified version from common/packages.yaml
@@ -49,25 +50,28 @@
                     f"WARNING: '{concrete_name}' concretized version {concrete_version} does not match {config_version} specified in $SPACK_ENV/common/packages.yaml"
                 )
         # Check whether concretized variants match settings from common/packages.yaml
-        config_variants = packages_versions["packages"][concrete_name]["variants"].split()
-        for config_variant in config_variants:
-            variant_mismatch = False
-            # Boolean variant
-            if config_variant[0] in ("+", "~"):
-                config_value = config_variant[0]=="+"
-                if concrete_spec["parameters"][config_variant[1:]] != config_value:
-                    variant_mismatch = True
-            # Named variant
-            elif "=" in config_variant:
-                config_variant, config_value = config_variant.split("=")
-                concrete_values = concrete_spec["parameters"][config_variant]
-                if type(concrete_values) is str:
-                     concrete_values = [concrete_values]
-                if set(config_value.split(",")) != set(concrete_values):
-                     variant_mismatch = True
-            if variant_mismatch:
-                iret = 1
-                print(f"WARNING: '{concrete_name}' concretized variant '{config_variant}' does not match configured value in $SPACK_ENV/common/packages.yaml")
+        if "variants" in packages_versions["packages"][concrete_name].keys():
+            config_variants = packages_versions["packages"][concrete_name]["variants"].split()
+            for config_variant in config_variants:
+                variant_mismatch = False
+                # Boolean variant
+                if config_variant[0] in ("+", "~"):
+                    config_value = config_variant[0] == "+"
+                    if concrete_spec["parameters"][config_variant[1:]] != config_value:
+                        variant_mismatch = True
+                # Named variant
+                elif "=" in config_variant:
+                    config_variant, config_value = config_variant.split("=")
+                    concrete_values = concrete_spec["parameters"][config_variant]
+                    if type(concrete_values) is str:
+                        concrete_values = [concrete_values]
+                    if set(config_value.split(",")) != set(concrete_values):
+                        variant_mismatch = True
+                if variant_mismatch:
+                    iret = 1
+                    print(
+                        f"WARNING: '{concrete_name}' concretized variant '{config_variant}' does not match configured value in $SPACK_ENV/common/packages.yaml"
+                    )
     # Check whether concretized package is an external based on site/packages.yaml
     if concrete_name in packages_externals["packages"].keys():
         is_external_config = "externals" in packages_externals["packages"][concrete_name].keys()