diff --git a/src/types/mapper.ts b/src/types/mapper.ts
index 89d7599..b4786f4 100644
--- a/src/types/mapper.ts
+++ b/src/types/mapper.ts
@@ -1,15 +1,29 @@
-import { ExtractSourceKeys, ExtractSources, ExtractDestinationKeys, ExtractDestinations, Profile } from '@/types/profile'
+import { ExtractSourceKeys, Profile } from '@/types/profile'
+
+/**
+ * Registered profiles grouped once by source key, then destination key, so each `map` call is two
+ * property lookups rather than a fresh pass over every registered profile.
+ */
+type ProfileIndex<TProfile> = {
+  [TSourceKey in ExtractSourceKeys<TProfile>]: {
+    [TMatch in Extract<TProfile, { sourceKey: TSourceKey }> as TMatch extends Profile ? TMatch['destinationKey'] : never]: TMatch
+  }
+}
+
+type ProfileSource<TProfile> = TProfile extends Profile<string, infer TSource, string, unknown> ? TSource : never
+
+type ProfileDestination<TProfile> = TProfile extends Profile<string, never, string, infer TDestination> ? TDestination : never
 
 export type Mapper<TProfiles extends readonly Profile[], TProfile = TProfiles[number]> = {
   register: (profiles: Profile[] | readonly Profile[] | Profile) => void,
   clear: () => void,
   has: (sourceKey: string, destinationKey: string) => boolean,
   map: <
-    TSourceKey extends ExtractSourceKeys<TProfile>,
-    TDestinationKey extends ExtractDestinationKeys<TProfile, TSourceKey>
-  > (sourceKey: TSourceKey, source: ExtractSources<TProfile, TSourceKey>, destinationKey: TDestinationKey) => ExtractDestinations<TProfile, TSourceKey, TDestinationKey>,
+    TSourceKey extends keyof ProfileIndex<TProfile> & string,
+    TDestinationKey extends keyof ProfileIndex<TProfile>[TSourceKey] & string
+  > (sourceKey: TSourceKey, source: ProfileSource<ProfileIndex<TProfile>[TSourceKey][TDestinationKey]>, destinationKey: TDestinationKey) => ProfileDestination<ProfileIndex<TProfile>[TSourceKey][TDestinationKey]>,
   mapMany: <
-    TSourceKey extends ExtractSourceKeys<TProfile>,
-    TDestinationKey extends ExtractDestinationKeys<TProfile, TSourceKey>
-  > (sourceKey: TSourceKey, sourceArray: ExtractSources<TProfile, TSourceKey>[], destinationKey: TDestinationKey) => ExtractDestinations<TProfile, TSourceKey, TDestinationKey>[],
+    TSourceKey extends keyof ProfileIndex<TProfile> & string,
+    TDestinationKey extends keyof ProfileIndex<TProfile>[TSourceKey] & string
+  > (sourceKey: TSourceKey, sourceArray: ProfileSource<ProfileIndex<TProfile>[TSourceKey][TDestinationKey]>[], destinationKey: TDestinationKey) => ProfileDestination<ProfileIndex<TProfile>[TSourceKey][TDestinationKey]>[],
 }