diff --git a/src/github.com/matrix-org/dendrite/clientapi/auth/storage/accounts/storage.go b/src/github.com/matrix-org/dendrite/clientapi/auth/storage/accounts/storage.go
index d5712eb50..addb6a9d2 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/auth/storage/accounts/storage.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/auth/storage/accounts/storage.go
@@ -24,7 +24,7 @@ import (
 	"github.com/matrix-org/gomatrixserverlib"
 	"golang.org/x/crypto/bcrypt"
 	// Import the postgres database driver.
-	_ "github.com/lib/pq"
+	"github.com/lib/pq"
 )
 
 // Database represents an account database
@@ -118,7 +118,8 @@ func (d *Database) SetDisplayName(
 }
 
 // CreateAccount makes a new account with the given login name and password, and creates an empty profile
-// for this account. If no password is supplied, the account will be a passwordless account.
+// for this account. If no password is supplied, the account will be a passwordless account. If the
+// account already exists, it will return nil, nil.
 func (d *Database) CreateAccount(
 	ctx context.Context, localpart, plaintextPassword string,
 ) (*authtypes.Account, error) {
@@ -127,6 +128,12 @@ func (d *Database) CreateAccount(
 		return nil, err
 	}
 	if err := d.profiles.insertProfile(ctx, localpart); err != nil {
+		if err, ok := err.(*pq.Error); ok {
+			if err.Code.Class() == "23" {
+				// 23 => unique_violation => Account already exists
+				return nil, nil
+			}
+		}
 		return nil, err
 	}
 	return d.accounts.insertAccount(ctx, localpart, hash)
diff --git a/src/github.com/matrix-org/dendrite/clientapi/routing/register.go b/src/github.com/matrix-org/dendrite/clientapi/routing/register.go
index 6bcff84a3..3068f521d 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/routing/register.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/routing/register.go
@@ -457,25 +457,17 @@ func completeRegistration(
 		}
 	}
 
-	avail, err := accountDB.CheckAccountAvailability(ctx, username)
-	if err == nil && !avail {
-		return util.JSONResponse{
-			Code: 400,
-			JSON: jsonerror.UserInUse("Desired user ID is already taken."),
-		}
-	} else if err != nil {
-		return util.JSONResponse{
-			Code: 500,
-			JSON: jsonerror.Unknown("Failed to check account availability: " + err.Error()),
-		}
-	}
-
 	acc, err := accountDB.CreateAccount(ctx, username, password)
 	if err != nil {
 		return util.JSONResponse{
 			Code: 500,
 			JSON: jsonerror.Unknown("failed to create account: " + err.Error()),
 		}
+	} else if acc == nil {
+		return util.JSONResponse{
+			Code: 400,
+			JSON: jsonerror.UserInUse("Desired user ID is already taken."),
+		}
 	}
 
 	token, err := auth.GenerateAccessToken()