diff --git a/Sources/StructuredQueriesCore/QueryFragmentBuilder.swift b/Sources/StructuredQueriesCore/QueryFragmentBuilder.swift
index d029e44a..19e7e1ed 100644
--- a/Sources/StructuredQueriesCore/QueryFragmentBuilder.swift
+++ b/Sources/StructuredQueriesCore/QueryFragmentBuilder.swift
@@ -27,6 +27,12 @@ extension QueryFragmentBuilder<Bool> {
   ) -> [QueryFragment] {
     [expression.queryFragment]
   }
+
+  public static func buildExpression(
+    _ expression: some QueryExpression<some _OptionalPromotable<Bool?>>
+  ) -> [QueryFragment] {
+    [expression.queryFragment]
+  }
 }
 
 extension QueryFragmentBuilder<()> {
diff --git a/Sources/StructuredQueriesCore/ScalarFunctions.swift b/Sources/StructuredQueriesCore/ScalarFunctions.swift
index f999dcb0..56cef290 100644
--- a/Sources/StructuredQueriesCore/ScalarFunctions.swift
+++ b/Sources/StructuredQueriesCore/ScalarFunctions.swift
@@ -120,7 +120,8 @@ extension QueryExpression where QueryValue: FloatingPoint {
   }
 }
 
-extension QueryExpression where QueryValue: Numeric {
+extension QueryExpression
+where QueryValue: _OptionalPromotable, QueryValue._Optionalized.Wrapped: Numeric {
   /// Wraps this numeric query expression with the `abs` function.
   ///
   /// - Returns: An expression wrapped with the `abs` function.
@@ -251,14 +252,18 @@ extension QueryExpression where QueryValue == String {
   public func instr(_ occurrence: some QueryExpression<QueryValue>) -> some QueryExpression<Int> {
     QueryFunction("instr", self, occurrence)
   }
+}
 
+extension QueryExpression where QueryValue: _OptionalPromotable<String?> {
   /// Wraps this string expression with the `lower` function.
   ///
   /// - Returns: An expression wrapped with the `lower` function.
   public func lower() -> some QueryExpression<QueryValue> {
     QueryFunction("lower", self)
   }
+}
 
+extension QueryExpression where QueryValue == String {
   /// Wraps this string expression with the `ltrim` function.
   ///
   /// - Parameter characters: Characters to trim.
@@ -279,14 +284,18 @@ extension QueryExpression where QueryValue == String {
   public func octetLength() -> some QueryExpression<Int> {
     QueryFunction("octet_length", self)
   }
+}
 
+extension QueryExpression where QueryValue: _OptionalPromotable<String?> {
   /// Wraps this string expression with the `quote` function.
   ///
   /// - Returns: An expression wrapped with the `quote` function.
   public func quote() -> some QueryExpression<QueryValue> {
     QueryFunction("quote", self)
   }
+}
 
+extension QueryExpression where QueryValue == String {
   /// Creates an expression invoking the `replace` function.
   ///
   /// - Parameters:
@@ -346,13 +355,15 @@ extension QueryExpression where QueryValue == String {
       return QueryFunction("trim", self)
     }
   }
+}
 
+extension QueryExpression where QueryValue: _OptionalPromotable<String?> {
   /// Wraps this string query expression with the `unhex` function.
   ///
   /// - Parameter characters: Non-hexadecimal characters to skip.
   /// - Returns: An optional blob expression of the `unhex` function wrapping this expression.
   public func unhex(
-    _ characters: (some QueryExpression<QueryValue>)? = QueryValue?.none
+    _ characters: (some QueryExpression<String>)? = String?.none
   ) -> some QueryExpression<[UInt8]?> {
     if let characters {
       return QueryFunction("unhex", self, characters)
diff --git a/Sources/StructuredQueriesCore/Statements/Delete.swift b/Sources/StructuredQueriesCore/Statements/Delete.swift
index 3d2898de..4595dbe7 100644
--- a/Sources/StructuredQueriesCore/Statements/Delete.swift
+++ b/Sources/StructuredQueriesCore/Statements/Delete.swift
@@ -48,7 +48,9 @@ public struct Delete<From: Table, Returning> {
   ///
   /// - Parameter keyPath: A key path to a Boolean expression to filter by.
   /// - Returns: A statement with the added predicate.
-  public func `where`(_ keyPath: KeyPath<From.TableColumns, some QueryExpression<Bool>>) -> Self {
+  public func `where`(
+    _ keyPath: KeyPath<From.TableColumns, some QueryExpression<some _OptionalPromotable<Bool?>>>
+  ) -> Self {
     var update = self
     update.where.append(From.columns[keyPath: keyPath].queryFragment)
     return update
@@ -64,7 +66,9 @@ public struct Delete<From: Table, Returning> {
   /// - Parameter predicate: A closure that returns a Boolean expression to filter by.
   /// - Returns: A statement with the added predicate.
   @_disfavoredOverload
-  public func `where`(_ predicate: (From.TableColumns) -> some QueryExpression<Bool>) -> Self {
+  public func `where`(
+    _ predicate: (From.TableColumns) -> some QueryExpression<some _OptionalPromotable<Bool?>>
+  ) -> Self {
     var update = self
     update.where.append(predicate(From.columns).queryFragment)
     return update
diff --git a/Sources/StructuredQueriesCore/Statements/Select.swift b/Sources/StructuredQueriesCore/Statements/Select.swift
index fcb11d0b..2a356537 100644
--- a/Sources/StructuredQueriesCore/Statements/Select.swift
+++ b/Sources/StructuredQueriesCore/Statements/Select.swift
@@ -236,7 +236,7 @@ extension Table {
   ///   columns.
   /// - Returns: A select statement that is filtered by the given predicate.
   public static func having(
-    _ predicate: (TableColumns) -> some QueryExpression<Bool>
+    _ predicate: (TableColumns) -> some QueryExpression<some _OptionalPromotable<Bool?>>
   ) -> SelectOf<Self> {
     Where().having(predicate)
   }
@@ -1110,7 +1110,7 @@ extension Select {
   /// - Parameter keyPath: A key path from this select's table to a Boolean expression to filter by.
   /// - Returns: A new select statement that appends the given predicate to its `WHERE` clause.
   public func `where`(
-    _ keyPath: KeyPath<From.TableColumns, some QueryExpression<Bool>>
+    _ keyPath: KeyPath<From.TableColumns, some QueryExpression<some _OptionalPromotable<Bool?>>>
   ) -> Self
   where Joins == () {
     var select = self
@@ -1125,7 +1125,9 @@ extension Select {
   /// - Returns: A new select statement that appends the given predicate to its `WHERE` clause.
   @_disfavoredOverload
   public func `where`<each J: Table>(
-    _ predicate: (From.TableColumns, repeat (each J).TableColumns) -> some QueryExpression<Bool>
+    _ predicate: (From.TableColumns, repeat (each J).TableColumns) -> some QueryExpression<
+      some _OptionalPromotable<Bool?>
+    >
   ) -> Self
   where Joins == (repeat each J) {
     var select = self
@@ -1218,7 +1220,9 @@ extension Select {
   /// - Returns: A new select statement that appends the given predicate to its `HAVING` clause.
   @_disfavoredOverload
   public func having<each J: Table>(
-    _ predicate: (From.TableColumns, repeat (each J).TableColumns) -> some QueryExpression<Bool>
+    _ predicate: (From.TableColumns, repeat (each J).TableColumns) -> some QueryExpression<
+      some _OptionalPromotable<Bool?>
+    >
   ) -> Self
   where Joins == (repeat each J) {
     var select = self
diff --git a/Sources/StructuredQueriesCore/Statements/SelectStatement.swift b/Sources/StructuredQueriesCore/Statements/SelectStatement.swift
index 6cda833b..ce7ef301 100644
--- a/Sources/StructuredQueriesCore/Statements/SelectStatement.swift
+++ b/Sources/StructuredQueriesCore/Statements/SelectStatement.swift
@@ -47,7 +47,7 @@ public typealias SelectStatementOf<From: Table, each Join: Table> =
 
 extension SelectStatement {
   public static func `where`<From>(
-    _ predicate: (From.TableColumns) -> some QueryExpression<Bool>
+    _ predicate: (From.TableColumns) -> some QueryExpression<some _OptionalPromotable<Bool?>>
   ) -> Self
   where Self == Where<From> {
     Self(predicates: [predicate(From.columns).queryFragment])
diff --git a/Sources/StructuredQueriesCore/Statements/Update.swift b/Sources/StructuredQueriesCore/Statements/Update.swift
index 685bdf77..6ab67078 100644
--- a/Sources/StructuredQueriesCore/Statements/Update.swift
+++ b/Sources/StructuredQueriesCore/Statements/Update.swift
@@ -105,7 +105,9 @@ public struct Update<From: Table, Returning> {
   ///
   /// - Parameter keyPath: A key path to a Boolean expression to filter by.
   /// - Returns: A statement with the added predicate.
-  public func `where`(_ keyPath: KeyPath<From.TableColumns, some QueryExpression<Bool>>) -> Self {
+  public func `where`(
+    _ keyPath: KeyPath<From.TableColumns, some QueryExpression<some _OptionalPromotable<Bool?>>>
+  ) -> Self {
     var update = self
     update.where.append(From.columns[keyPath: keyPath].queryFragment)
     return update
@@ -117,7 +119,7 @@ public struct Update<From: Table, Returning> {
   /// - Returns: A statement with the added predicate.
   @_disfavoredOverload
   public func `where`(
-    _ predicate: (From.TableColumns) -> some QueryExpression<Bool>
+    _ predicate: (From.TableColumns) -> some QueryExpression<some _OptionalPromotable<Bool?>>
   ) -> Self {
     var update = self
     update.where.append(predicate(From.columns).queryFragment)
diff --git a/Sources/StructuredQueriesCore/Statements/Where.swift b/Sources/StructuredQueriesCore/Statements/Where.swift
index 5960d958..2e1704d0 100644
--- a/Sources/StructuredQueriesCore/Statements/Where.swift
+++ b/Sources/StructuredQueriesCore/Statements/Where.swift
@@ -20,7 +20,7 @@ extension Table {
   /// - Parameter keyPath: A key path to a Boolean expression to filter by.
   /// - Returns: A `WHERE` clause.
   public static func `where`(
-    _ keyPath: KeyPath<TableColumns, some QueryExpression<Bool>>
+    _ keyPath: KeyPath<TableColumns, some QueryExpression<some _OptionalPromotable<Bool?>>>
   ) -> Where<Self> {
     Where(predicates: [columns[keyPath: keyPath].queryFragment])
   }
@@ -33,7 +33,7 @@ extension Table {
   /// - Returns: A `WHERE` clause.
   @_disfavoredOverload
   public static func `where`(
-    _ predicate: (TableColumns) -> some QueryExpression<Bool>
+    _ predicate: (TableColumns) -> some QueryExpression<some _OptionalPromotable<Bool?>>
   ) -> Where<Self> {
     Where(predicates: [predicate(columns).queryFragment])
   }
@@ -292,7 +292,7 @@ extension Where: SelectStatement {
   /// - Parameter keyPath: A key path to a Boolean expression to filter by.
   /// - Returns: A where clause with the added predicate.
   public func `where`(
-    _ keyPath: KeyPath<From.TableColumns, some QueryExpression<Bool>>
+    _ keyPath: KeyPath<From.TableColumns, some QueryExpression<some _OptionalPromotable<Bool?>>>
   ) -> Self {
     var `where` = self
     `where`.predicates.append(From.columns[keyPath: keyPath].queryFragment)
@@ -305,7 +305,7 @@ extension Where: SelectStatement {
   /// - Returns: A where clause with the added predicate.
   @_disfavoredOverload
   public func `where`(
-    _ predicate: (From.TableColumns) -> some QueryExpression<Bool>
+    _ predicate: (From.TableColumns) -> some QueryExpression<some _OptionalPromotable<Bool?>>
   ) -> Self {
     var `where` = self
     `where`.predicates.append(predicate(From.columns).queryFragment)
@@ -409,7 +409,7 @@ extension Where: SelectStatement {
 
   /// A select statement for the filtered table with the given `HAVING` clause.
   public func having(
-    _ predicate: (From.TableColumns) -> some QueryExpression<Bool>
+    _ predicate: (From.TableColumns) -> some QueryExpression<some _OptionalPromotable<Bool?>>
   ) -> SelectOf<From> {
     asSelect().having(predicate)
   }
diff --git a/Tests/StructuredQueriesTests/WhereTests.swift b/Tests/StructuredQueriesTests/WhereTests.swift
index e0b61e15..ca72bcf9 100644
--- a/Tests/StructuredQueriesTests/WhereTests.swift
+++ b/Tests/StructuredQueriesTests/WhereTests.swift
@@ -1,6 +1,8 @@
+import Dependencies
 import Foundation
 import InlineSnapshotTesting
 import StructuredQueries
+import StructuredQueriesSQLite
 import Testing
 
 extension SnapshotTests {
@@ -109,5 +111,30 @@ extension SnapshotTests {
         """
       }
     }
+
+    @Test func optionalBoolean() throws {
+      @Dependency(\.defaultDatabase) var db
+      let remindersListIDs = try db.execute(
+        RemindersList.insert {
+          RemindersList.Draft(title: "New list")
+        }
+        .returning(\.id)
+      )
+      let remindersListID = try #require(remindersListIDs.first)
+
+      assertQuery(
+        RemindersList
+          .find(remindersListID)
+          .leftJoin(Reminder.all) { $0.id.eq($1.remindersListID) }
+          .where { $1.isCompleted }
+      ) {
+        """
+        SELECT "remindersLists"."id", "remindersLists"."color", "remindersLists"."title", "reminders"."id", "reminders"."assignedUserID", "reminders"."dueDate", "reminders"."isCompleted", "reminders"."isFlagged", "reminders"."notes", "reminders"."priority", "reminders"."remindersListID", "reminders"."title"
+        FROM "remindersLists"
+        LEFT JOIN "reminders" ON ("remindersLists"."id" = "reminders"."remindersListID")
+        WHERE ("remindersLists"."id" = 4) AND "reminders"."isCompleted"
+        """
+      }
+    }
   }
 }