diff --git a/lib/versioning/npm/index.ts b/lib/versioning/npm/index.ts
index a2e5f39669e8c210eb263f0ffcbfdf3a6bbb4b14..b2827405c16b8b53b1c97fce70c99a036357322e 100644
--- a/lib/versioning/npm/index.ts
+++ b/lib/versioning/npm/index.ts
@@ -35,7 +35,7 @@ export const isVersion = (input: string): string => valid(input);
 
 const isSingleVersion = (constraint: string): string =>
   isVersion(constraint) ||
-  (constraint.startsWith('=') && isVersion(constraint.substring(1).trim()));
+  (constraint?.startsWith('=') && isVersion(constraint.substring(1).trim()));
 
 export const api: VersioningApi = {
   equals,
diff --git a/lib/versioning/pep440/index.ts b/lib/versioning/pep440/index.ts
index 464abc75d9091fa38ec42b01fda912e390f70888..4440569fbb030e0be6f3ef616e2875ce06f220ee 100644
--- a/lib/versioning/pep440/index.ts
+++ b/lib/versioning/pep440/index.ts
@@ -46,7 +46,7 @@ const minSatisfyingVersion = (versions: string[], range: string): string => {
 
 export const isSingleVersion = (constraint: string): string =>
   isVersion(constraint) ||
-  (constraint.startsWith('==') && isVersion(constraint.substring(2).trim()));
+  (constraint?.startsWith('==') && isVersion(constraint.substring(2).trim()));
 
 export { isVersion, matches };