diff --git a/keyserver/src/creators/account-creator.js b/keyserver/src/creators/account-creator.js
--- a/keyserver/src/creators/account-creator.js
+++ b/keyserver/src/creators/account-creator.js
@@ -112,12 +112,10 @@
     VALUES ${[newUserRow]}
   `;
 
-  const { primaryIdentityPublicKey } = request;
   const [userViewerData] = await Promise.all([
     createNewUserCookie(id, {
       platformDetails: request.platformDetails,
       deviceToken,
-      primaryIdentityPublicKey,
     }),
     deleteCookie(viewer.cookieID),
     dbQuery(newUserQuery),
@@ -207,7 +205,6 @@
   +calendarQuery: CalendarQuery,
   +deviceTokenUpdateRequest?: ?DeviceTokenUpdateRequest,
   +platformDetails: PlatformDetails,
-  +primaryIdentityPublicKey: ?string,
   +socialProof: SIWESocialProof,
 };
 // Note: `processSIWEAccountCreation(...)` assumes that the validity of
@@ -233,7 +230,6 @@
     createNewUserCookie(id, {
       platformDetails: request.platformDetails,
       deviceToken,
-      primaryIdentityPublicKey: request.primaryIdentityPublicKey,
       socialProof: request.socialProof,
     }),
     deleteCookie(viewer.cookieID),
diff --git a/keyserver/src/responders/user-responders.js b/keyserver/src/responders/user-responders.js
--- a/keyserver/src/responders/user-responders.js
+++ b/keyserver/src/responders/user-responders.js
@@ -197,6 +197,8 @@
   calendarQuery: t.maybe(newEntryQueryInputValidator),
   deviceTokenUpdateRequest: t.maybe(deviceTokenUpdateRequestInputValidator),
   platformDetails: tPlatformDetails,
+  // We include `primaryIdentityPublicKey` to avoid breaking
+  // old clients, but we no longer do anything with it.
   primaryIdentityPublicKey: t.maybe(tRegex(primaryIdentityPublicKeyRegex)),
 });
 
@@ -214,21 +216,13 @@
   +input: any,
   +userID: string,
   +calendarQuery: ?CalendarQuery,
-  +primaryIdentityPublicKey?: ?string,
   +socialProof?: ?SIWESocialProof,
 };
 
 async function processSuccessfulLogin(
   params: ProcessSuccessfulLoginParams,
 ): Promise<LogInResponse> {
-  const {
-    viewer,
-    input,
-    userID,
-    calendarQuery,
-    primaryIdentityPublicKey,
-    socialProof,
-  } = params;
+  const { viewer, input, userID, calendarQuery, socialProof } = params;
 
   const request: LogInRequest = input;
   const newServerTime = Date.now();
@@ -239,7 +233,6 @@
     createNewUserCookie(userID, {
       platformDetails: request.platformDetails,
       deviceToken,
-      primaryIdentityPublicKey,
       socialProof,
     }),
     fetchNotAcknowledgedPolicies(userID, baseLegalPolicies),
@@ -464,6 +457,7 @@
   //    if it was included. We expect it to be included for native clients,
   //    and we expect it to be EXCLUDED for web clients.
   const { statement } = siweMessage;
+  // eslint-disable-next-line no-unused-vars
   const primaryIdentityPublicKey =
     statement && isValidSIWEStatementWithPublicKey(statement)
       ? getPublicKeyFromSIWEStatement(statement)
@@ -485,7 +479,6 @@
       calendarQuery,
       deviceTokenUpdateRequest,
       platformDetails,
-      primaryIdentityPublicKey,
       socialProof,
     };
     userID = await processSIWEAccountCreation(
@@ -500,7 +493,6 @@
     input,
     userID,
     calendarQuery,
-    primaryIdentityPublicKey,
     socialProof,
   });
 }
diff --git a/keyserver/src/session/cookies.js b/keyserver/src/session/cookies.js
--- a/keyserver/src/session/cookies.js
+++ b/keyserver/src/session/cookies.js
@@ -648,7 +648,6 @@
 type UserCookieCreationParams = {
   platformDetails: PlatformDetails,
   deviceToken?: ?string,
-  primaryIdentityPublicKey?: ?string,
   socialProof?: ?SIWESocialProof,
 };
 
@@ -663,12 +662,7 @@
   userID: string,
   params: UserCookieCreationParams,
 ): Promise<UserViewerData> {
-  const {
-    platformDetails,
-    deviceToken,
-    primaryIdentityPublicKey,
-    socialProof,
-  } = params;
+  const { platformDetails, deviceToken, socialProof } = params;
   const { platform, ...versions } = platformDetails || defaultPlatformDetails;
   const versionsString =
     Object.keys(versions).length > 0 ? JSON.stringify(versions) : null;
@@ -690,12 +684,11 @@
     time,
     deviceToken,
     versionsString,
-    primaryIdentityPublicKey,
     JSON.stringify(socialProof),
   ];
   const query = SQL`
     INSERT INTO cookies(id, hash, user, platform, creation_time, last_used,
-      device_token, versions, public_key, social_proof)
+      device_token, versions, social_proof)
     VALUES ${[cookieRow]}
   `;
   await dbQuery(query);
diff --git a/lib/types/account-types.js b/lib/types/account-types.js
--- a/lib/types/account-types.js
+++ b/lib/types/account-types.js
@@ -53,7 +53,6 @@
   +calendarQuery?: ?CalendarQuery,
   +deviceTokenUpdateRequest?: ?DeviceTokenUpdateRequest,
   +platformDetails: PlatformDetails,
-  +primaryIdentityPublicKey?: ?string,
 };
 
 export type RegisterResponse = {