diff --git a/.github/CHANGELOG.md b/.github/CHANGELOG.md
index d186b53b9..2413e79ef 100644
--- a/.github/CHANGELOG.md
+++ b/.github/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## [UNRELEASED]
 
+- Ensure that the variable designating a switch as primary is always initialized.
+
 ## [1.8.0]
 
 - Move NMN/HMN/MTL to new vrf, move CMN/CHN/CAN to default vrf.
diff --git a/canu/generate/switch/config/config.py b/canu/generate/switch/config/config.py
index 289371106..491bc4a0f 100644
--- a/canu/generate/switch/config/config.py
+++ b/canu/generate/switch/config/config.py
@@ -1519,9 +1519,10 @@ def get_switch_nodes(
             }
             nodes.append(new_node)
         elif shasta_name == "sw-spine":
+            is_primary, primary, secondary = switch_is_primary(switch_name)
+
             # sw-leaf ==> sw-spine
             if switch_name.startswith("sw-leaf"):
-                is_primary, primary, secondary = switch_is_primary(switch_name)
                 digits = re.findall(r"(\d+)", primary)[0]
                 lag_number = 100 + int(digits)
 
@@ -1539,10 +1540,8 @@ def get_switch_nodes(
 
             # sw-spine ==> sw-spine
             elif switch_name.startswith("sw-spine"):
-                is_primary, primary, secondary = switch_is_primary(switch_name)
                 lag_number = 256
             elif switch_name.startswith("sw-edge"):
-                is_primary, primary, secondary = switch_is_primary(switch_name)
                 lag_number = 250
             new_node = {
                 "subtype": "spine",