diff --git a/Sources/Partial/PartialConvertible.swift b/Sources/Partial/PartialConvertible.swift
index c67bccd6..776b3a71 100644
--- a/Sources/Partial/PartialConvertible.swift
+++ b/Sources/Partial/PartialConvertible.swift
@@ -10,6 +10,6 @@ public protocol PartialConvertible {
     /// ```
     ///
     /// - Parameter partial: The partial to retrieve values from
-    init(partial: Partial<Self>) throws
+    init<PartialType: PartialProtocol>(partial: PartialType) throws where PartialType.Wrapped == Self
 
 }
diff --git a/Sources/Partial/PartialProtocol.swift b/Sources/Partial/PartialProtocol.swift
index 5ab1a5e8..b84be190 100644
--- a/Sources/Partial/PartialProtocol.swift
+++ b/Sources/Partial/PartialProtocol.swift
@@ -31,26 +31,66 @@ public protocol PartialProtocol {
 
 extension PartialProtocol {
 
-    /// Attempts to update the stored value for the given key path by unwrapping the
-    /// provided partial value. If the unwrapping fails the error will be thrown.
+    /// Attempts to update the stored value for the given key path by unwrapping the provided partial value. If the
+    /// unwrapping fails the error will be thrown.
     ///
-    /// - Parameter value: A partial wrapping a value of type `Value`.
+    /// - Parameter partial: A partial wrapping a value of type `Value`.
     /// - Parameter keyPath: A key path from `Wrapped` to a property of type `Value`.
-    mutating func setValue<Value>(_ partial: Partial<Value>, for keyPath: KeyPath<Wrapped, Value>) throws where Value: PartialConvertible {
-        let value = try partial.unwrappedValue()
+    /// - Parameter unwrapper: A closure that will be called to unwrap the passed partial.
+    mutating func setValue<Value, PartialType>(
+        _ partial: PartialType,
+        for keyPath: KeyPath<Wrapped, Value>,
+        unwrapper: (_ partial: PartialType) throws -> Value
+    ) rethrows where PartialType: PartialProtocol, PartialType.Wrapped == Value {
+        let value = try unwrapper(partial)
         setValue(value, for: keyPath)
     }
 
-    /// Attempts to update the stored value for the given key path by unwrapping the
-    /// provided partial value. If the unwrapping fails the error will be thrown.
+    /// Attempts to update the stored value for the given key path by unwrapping the provided partial value. If the
+    /// unwrapping fails the error will be thrown.
     ///
-    /// - Parameter value: A partial wrapping a value of type `Value?`.
-    /// - Parameter keyPath: A key path from `Wrapped` to a property of type `Value`.
-    mutating func setValue<Value>(_ partial: Partial<Value>, for keyPath: KeyPath<Wrapped, Value?>) throws where Value: PartialConvertible {
-        let value = try partial.unwrappedValue()
+    /// - Parameter partial: A partial wrapping a value of type `Value`.
+    /// - Parameter keyPath: A key path from `Wrapped` to a property of type `Value?`.
+    /// - Parameter unwrapper: A closure that will be called to unwrap the passed partial.
+    mutating func setValue<Value, PartialType>(
+        _ partial: PartialType,
+        for keyPath: KeyPath<Wrapped, Value?>,
+        unwrapper: (_ partial: PartialType) throws -> Value
+    ) rethrows where PartialType: PartialProtocol, PartialType.Wrapped == Value {
+        let value = try unwrapper(partial)
         setValue(value, for: keyPath)
     }
 
+    /// Attempts to update the stored value for the given key path by unwrapping the provided partial value. If the
+    /// unwrapping fails the error will be thrown.
+    ///
+    /// - Parameter partial: A partial wrapping a value of type `Value`.
+    /// - Parameter keyPath: A key path from `Wrapped` to a property of type `Value`.
+    /// - Parameter unwrapper: A closure that will be called to unwrap the passed partial. Defaults to the
+    ///                        `init(partial:)` function of `Value`
+    mutating func setValue<Value, PartialType>(
+        _ partial: PartialType,
+        for keyPath: KeyPath<Wrapped, Value>,
+        customUnwrapper unwrapper: (_ partial: PartialType) throws -> Value = Value.init(partial:)
+    ) rethrows where PartialType: PartialProtocol, PartialType.Wrapped == Value, PartialType.Wrapped: PartialConvertible {
+        try setValue(partial, for: keyPath, unwrapper: unwrapper)
+    }
+
+    /// Attempts to update the stored value for the given key path by unwrapping the provided partial value. If the
+    /// unwrapping fails the error will be thrown.
+    ///
+    /// - Parameter partial: A partial wrapping a value of type `Value`.
+    /// - Parameter keyPath: A key path from `Wrapped` to a property of type `Value?`.
+    /// - Parameter unwrapper: A closure that will be called to unwrap the passed partial. Defaults to the
+    ///                        `init(partial:)` function of `Value`
+    mutating func setValue<Value, PartialType>(
+        _ partial: PartialType,
+        for keyPath: KeyPath<Wrapped, Value?>,
+        customUnwrapper unwrapper: (_ partial: PartialType) throws -> Value = Value.init(partial:)
+    ) rethrows where PartialType: PartialProtocol, PartialType.Wrapped == Value, PartialType.Wrapped: PartialConvertible {
+        try setValue(partial, for: keyPath, unwrapper: unwrapper)
+    }
+
     /// Retrieve or set a value for the given key path. Returns `nil` if the value has not been set. If the value is set
     /// to nil it will remove the value.
     ///
diff --git a/Tests/PartialTests/Models/StringWrapper.swift b/Tests/PartialTests/Models/StringWrapper.swift
index 139357fa..e8bfd8e6 100644
--- a/Tests/PartialTests/Models/StringWrapper.swift
+++ b/Tests/PartialTests/Models/StringWrapper.swift
@@ -1,13 +1,14 @@
 import Partial
 
 struct StringWrapper: PartialConvertible, Hashable, ExpressibleByStringLiteral {
+
     let string: String
 
     init(stringLiteral value: String) {
         self.string = value
     }
 
-    init(partial: Partial<StringWrapper>) throws {
+    init<PartialType: PartialProtocol>(partial: PartialType) throws where PartialType.Wrapped == StringWrapper {
         string = try partial.value(for: \.string)
     }
 }
diff --git a/Tests/PartialTests/Models/StringWrapperWrapper.swift b/Tests/PartialTests/Models/StringWrapperWrapper.swift
index 1bf79683..3e1b39e2 100644
--- a/Tests/PartialTests/Models/StringWrapperWrapper.swift
+++ b/Tests/PartialTests/Models/StringWrapperWrapper.swift
@@ -10,7 +10,7 @@ struct StringWrapperWrapper: PartialConvertible, Hashable {
         self.optionalStringWrapper = optionalStringWrapper
     }
 
-    init(partial: Partial<StringWrapperWrapper>) throws {
+    init<PartialType: PartialProtocol>(partial: PartialType) throws where PartialType.Wrapped == StringWrapperWrapper {
         stringWrapper = try partial.value(for: \.stringWrapper)
         optionalStringWrapper = try partial.value(for: \.optionalStringWrapper)
     }
diff --git a/Tests/PartialTests/Tests/Partial+PartialConvertibleTests.swift b/Tests/PartialTests/Tests/Partial+PartialConvertibleTests.swift
index 0802de8d..36d081af 100644
--- a/Tests/PartialTests/Tests/Partial+PartialConvertibleTests.swift
+++ b/Tests/PartialTests/Tests/Partial+PartialConvertibleTests.swift
@@ -72,6 +72,48 @@ final class Partial_PartialConvertibleTests: QuickSpec {
                         expect(partial[keyPath]) == unwrappedValue
                     }
                 }
+
+                context("set with a custom unwrapper") {
+                    context("that throws an error") {
+                        enum TestError: Error {
+                            case testError
+                        }
+
+                        var thrownError: Error!
+
+                        beforeEach {
+                            do {
+                                try partial.setValue(Partial<StringWrapper>(), for: keyPath) { _ in
+                                    throw TestError.testError
+                                }
+                            } catch {
+                                thrownError = error
+                            }
+                        }
+
+                        afterEach {
+                            thrownError = nil
+                        }
+
+                        it("should throw errors thrown by the unwrapper") {
+                            expect(thrownError).to(matchError(TestError.testError))
+                        }
+                    }
+
+                    context("that returns a value") {
+                        var returnedValue: StringWrapper!
+
+                        beforeEach {
+                            returnedValue = "returned value"
+                            partial.setValue(Partial<StringWrapper>(), for: keyPath) { _ in
+                                return returnedValue
+                            }
+                        }
+                        it("should set the key path to the value returned by the unwrapper") {
+                            expect(partial[keyPath]) == returnedValue
+                        }
+                    }
+                }
             }
 
             context("an optional key path") {
@@ -83,7 +125,7 @@ final class Partial_PartialConvertibleTests: QuickSpec {
                     partial.setValue(initialValue, for: keyPath)
                 }
 
-                context("set no an incomplete Partial") {
+                context("set to an incomplete Partial") {
                     var thrownError: Error?
 
                     beforeEach {
@@ -132,6 +174,48 @@ final class Partial_PartialConvertibleTests: QuickSpec {
                         expect(partial[keyPath]) == unwrappedValue
                     }
                 }
+
+                context("set with a custom unwrapper") {
+                    context("that throws an error") {
+                        enum TestError: Error {
+                            case testError
+                        }
+
+                        var thrownError: Error!
+
+                        beforeEach {
+                            do {
+                                try partial.setValue(Partial<StringWrapper>(), for: keyPath) { _ in
+                                    throw TestError.testError
+                                }
+                            } catch {
+                                thrownError = error
+                            }
+                        }
+
+                        afterEach {
+                            thrownError = nil
+                        }
+
+                        it("should throw errors thrown by the unwrapper") {
+                            expect(thrownError).to(matchError(TestError.testError))
+                        }
+                    }
+
+                    context("that returns a value") {
+                        var returnedValue: StringWrapper!
+
+                        beforeEach {
+                            returnedValue = "returned value"
+                            partial.setValue(Partial<StringWrapper>(), for: keyPath) { _ in
+                                return returnedValue
+                            }
+                        }
+                        it("should set the key path to the value returned by the unwrapper") {
+                            expect(partial[keyPath]) == returnedValue
+                        }
+                    }
+                }
             }
 
             context("unwrappedValue()") {
diff --git a/Tests/PartialTests/Tests/PartialBuilder+PartialConvertibleTests.swift b/Tests/PartialTests/Tests/PartialBuilder+PartialConvertibleTests.swift
index e71bbec1..01b61fc5 100644
--- a/Tests/PartialTests/Tests/PartialBuilder+PartialConvertibleTests.swift
+++ b/Tests/PartialTests/Tests/PartialBuilder+PartialConvertibleTests.swift
@@ -72,6 +72,48 @@ final class PartialBuilder_PartialConvertibleTests: QuickSpec {
                         expect(builder[keyPath]) == unwrappedValue
                     }
                 }
+
+                context("set with a custom unwrapper") {
+                    context("that throws an error") {
+                        enum TestError: Error {
+                            case testError
+                        }
+
+                        var thrownError: Error!
+
+                        beforeEach {
+                            do {
+                                try builder.setValue(Partial<StringWrapper>(), for: keyPath) { _ in
+                                    throw TestError.testError
+                                }
+                            } catch {
+                                thrownError = error
+                            }
+                        }
+
+                        afterEach {
+                            thrownError = nil
+                        }
+
+                        it("should throw errors thrown by the unwrapper") {
+                            expect(thrownError).to(matchError(TestError.testError))
+                        }
+                    }
+
+                    context("that returns a value") {
+                        var returnedValue: StringWrapper!
+
+                        beforeEach {
+                            returnedValue = "returned value"
+                            builder.setValue(Partial<StringWrapper>(), for: keyPath) { _ in
+                                return returnedValue
+                            }
+                        }
+                        it("should set the key path to the value returned by the unwrapper") {
+                            expect(builder[keyPath]) == returnedValue
+                        }
+                    }
+                }
             }
 
             context("an optional key path") {
@@ -132,6 +174,48 @@ final class PartialBuilder_PartialConvertibleTests: QuickSpec {
                         expect(builder[keyPath]) == unwrappedValue
                     }
                 }
+
+                context("set with a custom unwrapper") {
+                    context("that throws an error") {
+                        enum TestError: Error {
+                            case testError
+                        }
+
+                        var thrownError: Error!
+
+                        beforeEach {
+                            do {
+                                try builder.setValue(Partial<StringWrapper>(), for: keyPath) { _ in
+                                    throw TestError.testError
+                                }
+                            } catch {
+                                thrownError = error
+                            }
+                        }
+
+                        afterEach {
+                            thrownError = nil
+                        }
+
+                        it("should throw errors thrown by the unwrapper") {
+                            expect(thrownError).to(matchError(TestError.testError))
+                        }
+                    }
+
+                    context("that returns a value") {
+                        var returnedValue: StringWrapper!
+
+                        beforeEach {
+                            returnedValue = "returned value"
+                            builder.setValue(Partial<StringWrapper>(), for: keyPath) { _ in
+                                return returnedValue
+                            }
+                        }
+                        it("should set the key path to the value returned by the unwrapper") {
+                            expect(builder[keyPath]) == returnedValue
+                        }
+                    }
+                }
             }
 
             context("unwrappedValue()") {