diff --git a/package-lock.json b/package-lock.json
index ce33163399..d5ea0aacb1 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -17433,17 +17433,17 @@
       "integrity": "sha1-D3ca0W9IOuZfQoeWlCjp+8SqYYE="
     },
     "mongoose": {
-      "version": "5.11.10",
-      "resolved": "https://registry.npmjs.org/mongoose/-/mongoose-5.11.10.tgz",
-      "integrity": "sha512-daE2L6VW7WNywv7tL2KUkBViWvODbzr50Of1kJpIbzW3w3N5/TYcgSmhCsEDWfYGQXbun2rdd7+sOdsEC8zQSQ==",
+      "version": "5.12.3",
+      "resolved": "https://registry.npmjs.org/mongoose/-/mongoose-5.12.3.tgz",
+      "integrity": "sha512-frsSR9yeldaRpSUeTegXCSB0Tu5UGq8sHuHBuEV31Jk3COyxlKFQPL7UsdMhxPUCmk74FpOYSmNwxhWBEqgzQg==",
       "requires": {
         "@types/mongodb": "^3.5.27",
         "bson": "^1.1.4",
         "kareem": "2.3.2",
-        "mongodb": "3.6.3",
+        "mongodb": "3.6.5",
         "mongoose-legacy-pluralize": "1.0.2",
         "mpath": "0.8.3",
-        "mquery": "3.2.3",
+        "mquery": "3.2.5",
         "ms": "2.1.2",
         "regexp-clone": "1.0.0",
         "safe-buffer": "5.2.1",
@@ -17452,14 +17452,14 @@
       },
       "dependencies": {
         "bson": {
-          "version": "1.1.5",
-          "resolved": "https://registry.npmjs.org/bson/-/bson-1.1.5.tgz",
-          "integrity": "sha512-kDuEzldR21lHciPQAIulLs1LZlCXdLziXI6Mb/TDkwXhb//UORJNPXgcRs2CuO4H0DcMkpfT3/ySsP3unoZjBg=="
+          "version": "1.1.6",
+          "resolved": "https://registry.npmjs.org/bson/-/bson-1.1.6.tgz",
+          "integrity": "sha512-EvVNVeGo4tHxwi8L6bPj3y3itEvStdwvvlojVxxbyYfoaxJ6keLgrTuKdyfEAszFK+H3olzBuafE0yoh0D1gdg=="
         },
         "mongodb": {
-          "version": "3.6.3",
-          "resolved": "https://registry.npmjs.org/mongodb/-/mongodb-3.6.3.tgz",
-          "integrity": "sha512-rOZuR0QkodZiM+UbQE5kDsJykBqWi0CL4Ec2i1nrGrUI3KO11r6Fbxskqmq3JK2NH7aW4dcccBuUujAP0ERl5w==",
+          "version": "3.6.5",
+          "resolved": "https://registry.npmjs.org/mongodb/-/mongodb-3.6.5.tgz",
+          "integrity": "sha512-mQlYKw1iGbvJJejcPuyTaytq0xxlYbIoVDm2FODR+OHxyEiMR021vc32bTvamgBjCswsD54XIRwhg3yBaWqJjg==",
           "requires": {
             "bl": "^2.2.1",
             "bson": "^1.1.4",
@@ -17543,9 +17543,9 @@
       "integrity": "sha512-eb9rRvhDltXVNL6Fxd2zM9D4vKBxjVVQNLNijlj7uoXUy19zNDsIif5zR+pWmPCWNKwAtqyo4JveQm4nfD5+eA=="
     },
     "mquery": {
-      "version": "3.2.3",
-      "resolved": "https://registry.npmjs.org/mquery/-/mquery-3.2.3.tgz",
-      "integrity": "sha512-cIfbP4TyMYX+SkaQ2MntD+F2XbqaBHUYWk3j+kqdDztPWok3tgyssOZxMHMtzbV1w9DaSlvEea0Iocuro41A4g==",
+      "version": "3.2.5",
+      "resolved": "https://registry.npmjs.org/mquery/-/mquery-3.2.5.tgz",
+      "integrity": "sha512-VjOKHHgU84wij7IUoZzFRU07IAxd5kWJaDmyUzQlbjHjyoeK5TNeeo8ZsFDtTYnSgpW6n/nMNIHvE3u8Lbrf4A==",
       "requires": {
         "bluebird": "3.5.1",
         "debug": "3.1.0",
diff --git a/package.json b/package.json
index 73be391b0f..2b861f686d 100644
--- a/package.json
+++ b/package.json
@@ -125,7 +125,7 @@
     "lodash": "^4.17.21",
     "moment-timezone": "0.5.33",
     "mongodb-uri": "^0.9.7",
-    "mongoose": "^5.11.10",
+    "mongoose": "^5.12.3",
     "multiparty": ">=4.2.2",
     "neverthrow": "^4.2.1",
     "ng-infinite-scroll": "^1.3.0",
diff --git a/src/app/models/admin_verification.server.model.ts b/src/app/models/admin_verification.server.model.ts
index cbce56da2c..3f5d675999 100644
--- a/src/app/models/admin_verification.server.model.ts
+++ b/src/app/models/admin_verification.server.model.ts
@@ -12,7 +12,10 @@ import { USER_SCHEMA_ID } from './user.server.model'
 
 export const ADMIN_VERIFICATION_SCHEMA_ID = 'AdminVerification'
 
-const AdminVerificationSchema = new Schema<IAdminVerificationSchema>(
+const AdminVerificationSchema = new Schema<
+  IAdminVerificationSchema,
+  IAdminVerificationModel
+>(
   {
     admin: {
       type: Schema.Types.ObjectId,
diff --git a/src/app/models/form.server.model.ts b/src/app/models/form.server.model.ts
index aa8b879aed..460cb5765b 100644
--- a/src/app/models/form.server.model.ts
+++ b/src/app/models/form.server.model.ts
@@ -131,7 +131,7 @@ const EncryptedFormSchema = new Schema<IEncryptedFormSchema>({
   },
 })
 
-const EmailFormSchema = new Schema<IEmailFormSchema>({
+const EmailFormSchema = new Schema<IEmailFormSchema, IEmailFormModel>({
   emails: {
     type: [
       {
@@ -159,7 +159,7 @@ const compileFormModel = (db: Mongoose): IFormModel => {
   const User = getUserModel(db)
 
   // Schema
-  const FormSchema = new Schema<IFormSchema>(
+  const FormSchema = new Schema<IFormSchema, IFormModel>(
     {
       title: {
         type: String,
@@ -342,7 +342,7 @@ const compileFormModel = (db: Mongoose): IFormModel => {
   // Add discriminators for the various field types.
   const FormFieldPath = FormSchema.path(
     'form_fields',
-  ) as Schema.Types.DocumentArray
+  ) as Schema.Types.DocumentArrayWithLooseDiscriminator
 
   const TableFieldSchema = createTableFieldSchema()
 
@@ -376,7 +376,7 @@ const compileFormModel = (db: Mongoose): IFormModel => {
   FormFieldPath.discriminator(BasicField.Table, TableFieldSchema)
   const TableColumnPath = TableFieldSchema.path(
     'columns',
-  ) as Schema.Types.DocumentArray
+  ) as Schema.Types.DocumentArrayWithLooseDiscriminator
   TableColumnPath.discriminator(
     BasicField.ShortText,
     createShortTextFieldSchema(),
@@ -389,13 +389,13 @@ const compileFormModel = (db: Mongoose): IFormModel => {
   // Discriminator defines all possible values of startPage.logo
   const StartPageLogoPath = FormSchema.path(
     'startPage.logo',
-  ) as Schema.Types.DocumentArray
+  ) as Schema.Types.DocumentArrayWithLooseDiscriminator
   StartPageLogoPath.discriminator(FormLogoState.Custom, CustomFormLogoSchema)
 
   // Discriminator defines different logic types
   const FormLogicPath = FormSchema.path(
     'form_logics',
-  ) as Schema.Types.DocumentArray
+  ) as Schema.Types.DocumentArrayWithLooseDiscriminator
 
   FormLogicPath.discriminator(LogicType.ShowFields, ShowFieldsLogicSchema)
   FormLogicPath.discriminator(LogicType.PreventSubmit, PreventSubmitLogicSchema)
@@ -458,12 +458,6 @@ const compileFormModel = (db: Mongoose): IFormModel => {
     }
   }
 
-  FormSchema.methods.getSettings = function (
-    this: IFormDocument,
-  ): FormSettings {
-    return pick(this, FORM_SETTING_FIELDS)
-  }
-
   // Archives form.
   FormSchema.methods.archive = function (this: IFormSchema) {
     // Return instantly when form is already archived.
@@ -475,8 +469,16 @@ const compileFormModel = (db: Mongoose): IFormModel => {
     return this.save()
   }
 
+  const FormDocumentSchema = (FormSchema as unknown) as Schema<IFormDocument>
+
+  FormDocumentSchema.methods.getSettings = function (
+    this: IFormDocument,
+  ): FormSettings {
+    return pick(this, FORM_SETTING_FIELDS)
+  }
+
   // Transfer ownership of the form to another user
-  FormSchema.methods.transferOwner = async function (
+  FormDocumentSchema.methods.transferOwner = async function (
     this: IFormDocument,
     currentOwner: IUserSchema,
     newOwner: IUserSchema,
diff --git a/src/app/models/form_statistics_total.server.model.ts b/src/app/models/form_statistics_total.server.model.ts
index 573c61effb..212eaec6b7 100644
--- a/src/app/models/form_statistics_total.server.model.ts
+++ b/src/app/models/form_statistics_total.server.model.ts
@@ -12,7 +12,10 @@ const FORM_STATS_TOTAL_SCHEMA_ID = 'FormStatisticsTotal'
 const FORM_STATS_COLLECTION_NAME = 'formStatisticsTotal'
 
 const compileFormStatisticsTotalModel = (db: Mongoose) => {
-  const FormStatisticsTotalSchema = new Schema<IFormStatisticsTotalSchema>(
+  const FormStatisticsTotalSchema = new Schema<
+    IFormStatisticsTotalSchema,
+    IFormStatisticsTotalModel
+  >(
     {
       formId: {
         type: Schema.Types.ObjectId,
diff --git a/src/app/models/login.server.model.ts b/src/app/models/login.server.model.ts
index c0a2b1f8b5..b39a4b812b 100644
--- a/src/app/models/login.server.model.ts
+++ b/src/app/models/login.server.model.ts
@@ -14,7 +14,7 @@ import { USER_SCHEMA_ID } from './user.server.model'
 
 export const LOGIN_SCHEMA_ID = 'Login'
 
-const LoginSchema = new Schema<ILoginSchema>(
+const LoginSchema = new Schema<ILoginSchema, ILoginModel>(
   {
     admin: {
       type: Schema.Types.ObjectId,
@@ -133,7 +133,7 @@ LoginSchema.statics.aggregateLoginStats = function (
 }
 
 const compileLoginModel = (db: Mongoose) =>
-  db.model<ILoginSchema>(LOGIN_SCHEMA_ID, LoginSchema) as ILoginModel
+  db.model<ILoginSchema, ILoginModel>(LOGIN_SCHEMA_ID, LoginSchema)
 
 /**
  * Retrieves the Login model on the given Mongoose instance. If the model is
@@ -143,7 +143,7 @@ const compileLoginModel = (db: Mongoose) =>
  */
 const getLoginModel = (db: Mongoose): ILoginModel => {
   try {
-    return db.model(LOGIN_SCHEMA_ID) as ILoginModel
+    return db.model<ILoginSchema, ILoginModel>(LOGIN_SCHEMA_ID)
   } catch {
     return compileLoginModel(db)
   }
diff --git a/src/app/models/submission.server.model.ts b/src/app/models/submission.server.model.ts
index f27c02e9fb..0bf1b1b2d9 100644
--- a/src/app/models/submission.server.model.ts
+++ b/src/app/models/submission.server.model.ts
@@ -25,7 +25,7 @@ import { FORM_SCHEMA_ID } from './form.server.model'
 
 export const SUBMISSION_SCHEMA_ID = 'Submission'
 
-const SubmissionSchema = new Schema<ISubmissionSchema>(
+const SubmissionSchema = new Schema<ISubmissionSchema, ISubmissionModel>(
   {
     form: {
       type: Schema.Types.ObjectId,
@@ -143,7 +143,10 @@ const webhookResponseSchema = new Schema<IWebhookResponseSchema>(
   },
 )
 
-const EncryptSubmissionSchema = new Schema<IEncryptedSubmissionSchema>({
+const EncryptSubmissionSchema = new Schema<
+  IEncryptedSubmissionSchema,
+  IEncryptSubmissionModel
+>({
   encryptedContent: {
     type: String,
     trim: true,
@@ -347,15 +350,15 @@ const compileSubmissionModel = (db: Mongoose): ISubmissionModel => {
   const Submission = db.model('Submission', SubmissionSchema)
   Submission.discriminator(SubmissionType.Email, EmailSubmissionSchema)
   Submission.discriminator(SubmissionType.Encrypt, EncryptSubmissionSchema)
-  return db.model<ISubmissionSchema>(
+  return db.model<ISubmissionSchema, ISubmissionModel>(
     SUBMISSION_SCHEMA_ID,
     SubmissionSchema,
-  ) as ISubmissionModel
+  )
 }
 
 const getSubmissionModel = (db: Mongoose): ISubmissionModel => {
   try {
-    return db.model(SUBMISSION_SCHEMA_ID) as ISubmissionModel
+    return db.model<ISubmissionSchema, ISubmissionModel>(SUBMISSION_SCHEMA_ID)
   } catch {
     return compileSubmissionModel(db)
   }
diff --git a/src/app/models/token.server.model.ts b/src/app/models/token.server.model.ts
index f4d2538956..c07699a2b5 100644
--- a/src/app/models/token.server.model.ts
+++ b/src/app/models/token.server.model.ts
@@ -4,7 +4,7 @@ import { IToken, ITokenModel, ITokenSchema } from '../../types'
 
 export const TOKEN_SCHEMA_ID = 'Token'
 
-const TokenSchema = new Schema<ITokenSchema>({
+const TokenSchema = new Schema<ITokenSchema, ITokenModel>({
   email: {
     type: String,
     required: true,
diff --git a/src/app/models/user.server.model.ts b/src/app/models/user.server.model.ts
index f0fbfc20eb..84c334b4e7 100644
--- a/src/app/models/user.server.model.ts
+++ b/src/app/models/user.server.model.ts
@@ -18,7 +18,7 @@ export const USER_SCHEMA_ID = 'User'
 const compileUserModel = (db: Mongoose) => {
   const Agency = getAgencyModel(db)
 
-  const UserSchema: Schema<IUserSchema> = new Schema(
+  const UserSchema: Schema<IUserSchema, IUserModel> = new Schema(
     {
       email: {
         type: String,
@@ -59,7 +59,8 @@ const compileUserModel = (db: Mongoose) => {
             if (!phoneNumber) return false
             return phoneNumber.isValid()
           },
-          message: (props) => `${props.value} is not a valid mobile number`,
+          message: (props: { value: string }) =>
+            `${props.value} is not a valid mobile number`,
         },
       },
       lastAccessed: Date,
diff --git a/src/app/modules/bounce/bounce.model.ts b/src/app/modules/bounce/bounce.model.ts
index 8f1d9934d0..de7d7f4d47 100644
--- a/src/app/modules/bounce/bounce.model.ts
+++ b/src/app/modules/bounce/bounce.model.ts
@@ -23,7 +23,7 @@ export interface IBounceModel extends Model<IBounceSchema> {
   ) => IBounceSchema
 }
 
-const BounceSchema = new Schema<IBounceSchema>({
+const BounceSchema = new Schema<IBounceSchema, IBounceModel>({
   formId: {
     type: Schema.Types.ObjectId,
     ref: FORM_SCHEMA_ID,
diff --git a/src/app/modules/myinfo/myinfo_hash.model.ts b/src/app/modules/myinfo/myinfo_hash.model.ts
index bf53a7e406..03f95905f9 100644
--- a/src/app/modules/myinfo/myinfo_hash.model.ts
+++ b/src/app/modules/myinfo/myinfo_hash.model.ts
@@ -7,7 +7,7 @@ import { FORM_SCHEMA_ID } from '../../models/form.server.model'
 
 export const MYINFO_HASH_SCHEMA_ID = 'MyInfoHash'
 
-const MyInfoHashSchema = new Schema<IMyInfoHashSchema>(
+const MyInfoHashSchema = new Schema<IMyInfoHashSchema, IMyInfoHashModel>(
   {
     // We stored a hashed uinFin using a salt stored as a env var
     // Note: key name not updated to reflect this for backward compatibility purposes
diff --git a/src/app/modules/submission/submission.service.ts b/src/app/modules/submission/submission.service.ts
index 45f7ce5beb..50619491c7 100644
--- a/src/app/modules/submission/submission.service.ts
+++ b/src/app/modules/submission/submission.service.ts
@@ -227,7 +227,7 @@ export const getFormSubmissionsCount = (
  * @returns ok(true) if all emails were sent successfully
  * @returns err(SendEmailConfirmationError) if any email failed to be sent
  */
-export const sendEmailConfirmations = ({
+export const sendEmailConfirmations = <S extends ISubmissionSchema>({
   form,
   submission,
   parsedResponses,
@@ -235,7 +235,7 @@ export const sendEmailConfirmations = ({
   attachments,
 }: {
   form: IPopulatedForm
-  submission: ISubmissionSchema
+  submission: S
   parsedResponses: ProcessedFieldResponse[]
   autoReplyData?: EmailRespondentConfirmationField[]
   attachments?: IAttachmentInfo[]
diff --git a/src/app/modules/verification/verification.model.ts b/src/app/modules/verification/verification.model.ts
index e1be83a247..53d96c3d82 100644
--- a/src/app/modules/verification/verification.model.ts
+++ b/src/app/modules/verification/verification.model.ts
@@ -33,7 +33,10 @@ const VerificationFieldSchema = new Schema<IVerificationFieldSchema>({
 })
 
 const compileVerificationModel = (db: Mongoose): IVerificationModel => {
-  const VerificationSchema = new Schema<IVerificationSchema>({
+  const VerificationSchema = new Schema<
+    IVerificationSchema,
+    IVerificationModel
+  >({
     formId: {
       type: Schema.Types.ObjectId,
       ref: FORM_SCHEMA_ID,
diff --git a/src/app/services/sms/sms_count.server.model.ts b/src/app/services/sms/sms_count.server.model.ts
index ea27658a2f..e7638e2ac8 100644
--- a/src/app/services/sms/sms_count.server.model.ts
+++ b/src/app/services/sms/sms_count.server.model.ts
@@ -83,7 +83,7 @@ const BouncedSubmissionSmsCountSchema = new Schema<IBouncedSubmissionSmsCountSch
 )
 
 const compileSmsCountModel = (db: Mongoose) => {
-  const SmsCountSchema = new Schema<ISmsCountSchema>(
+  const SmsCountSchema = new Schema<ISmsCountSchema, ISmsCountModel>(
     {
       msgSrvcSid: {
         type: String,
diff --git a/src/types/vendor/mongoose.d.ts b/src/types/vendor/mongoose.d.ts
new file mode 100644
index 0000000000..917356050f
--- /dev/null
+++ b/src/types/vendor/mongoose.d.ts
@@ -0,0 +1,33 @@
+/**
+ * Additional type declarations for mongoose to fit our use case,
+ * to accommodate the non-standard but compatible use of types
+ * in schema registration
+ */
+declare module 'mongoose' {
+  namespace Schema {
+    namespace Types {
+      /**
+       * A DocumentArray with a discriminator function that takes in a
+       * type-generic Schema.
+       */
+      class DocumentArrayWithLooseDiscriminator extends DocumentArray {
+        /**
+         * In the built-in type declarations in
+         * version 5.12 of mongoose, discriminator() expects a Schema
+         * (and hence Schema<Document>). This does not work; a Schema
+         * for a subtype of Document is not a Schema for a Document, as
+         * Schema.methods expect to operate on the Schema's document type,
+         * which is not necessarily a Document.
+         *
+         * Address this by overriding the definition and provide a type-generic
+         * Schema argument.
+         */
+        discriminator<T extends Document>(
+          name: string,
+          schema: Schema<T>,
+          tag?: string,
+        ): unknown
+      }
+    }
+  }
+}