diff --git a/pygdsm/__init__.py b/pygdsm/__init__.py
index 7b53832..717e4f0 100644
--- a/pygdsm/__init__.py
+++ b/pygdsm/__init__.py
@@ -35,17 +35,18 @@ def init_gsm(gsm_name: str='gsm08'):
         sky_model (various): Corresponding sky model
     """
     gsm_name = gsm_name.lower().strip()
-    match gsm_name:
-        case 'gsm': # Shorthand for GSM08
-            return GlobalSkyModel()
-        case 'gsm08':
-            return GlobalSkyModel()
-        case 'gsm16':
-            return GlobalSkyModel16()
-        case 'lfsm':
-            return LowFrequencySkyModel()
-        case 'haslam':
-            return HaslamSkyModel()
+    if gsm_name == 'gsm': # Shorthand for GSM08
+        return GlobalSkyModel()
+    elif gsm_name == 'gsm08':
+        return GlobalSkyModel()
+    elif gsm_name == 'gsm16':
+        return GlobalSkyModel16()
+    elif gsm_name == 'lfsm':
+        return LowFrequencySkyModel()
+    elif gsm_name == 'haslam':
+        return HaslamSkyModel()
+    else:
+        raise ValueError(f'Invalid model specification "{gsm_name}"')
 
 
 def init_observer(gsm_name: str='gsm08'):
@@ -68,14 +69,16 @@ def init_observer(gsm_name: str='gsm08'):
         observer (various): Corresponding sky model observer
     """
     gsm_name = gsm_name.lower().strip()
-    match gsm_name:
-        case 'gsm': # Shorthand for GSM08
-            return GSMObserver()
-        case 'gsm08':
-            return GSMObserver()
-        case 'gsm16':
-            return GSMObserver16()
-        case 'lfsm':
-            return LFSMObserver()
-        case 'haslam':
-            return HaslamObserver()
\ No newline at end of file
+
+    if gsm_name == 'gsm': # Shorthand for GSM08
+        return GSMObserver()
+    elif gsm_name == 'gsm08':
+        return GSMObserver()
+    elif gsm_name == 'gsm16':
+        return GSMObserver16()
+    elif gsm_name == 'lfsm':
+        return LFSMObserver()
+    elif gsm_name == 'haslam':
+        return HaslamObserver()
+    else:
+        raise ValueError(f'Invalid model specification "{gsm_name}"')
\ No newline at end of file
diff --git a/setup.cfg b/setup.cfg
index 8b09a37..09c4c7c 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -7,6 +7,9 @@ universal=1
 [metadata]
 description_file=README.md
 
+[options]
+python_requires = >=3.6
+
 [aliases]
 test=pytest
 
diff --git a/setup.py b/setup.py
index 9a89064..dde423b 100644
--- a/setup.py
+++ b/setup.py
@@ -59,6 +59,10 @@
         # Specify the Python versions you support here. In particular, ensure
         # that you indicate whether you support Python 2, Python 3 or both.
         'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
+        'Programming Language :: Python :: 3.9',
         'Programming Language :: Python :: 3.10',
         'Programming Language :: Python :: 3.11',
     ],