diff --git a/Sources/SwiftCompilerPlugin/CompilerPlugin.swift b/Sources/SwiftCompilerPlugin/CompilerPlugin.swift
index 23a2b22cdb2..69766b44c73 100644
--- a/Sources/SwiftCompilerPlugin/CompilerPlugin.swift
+++ b/Sources/SwiftCompilerPlugin/CompilerPlugin.swift
@@ -63,7 +63,8 @@ public protocol CompilerPlugin {
 }
 
 extension CompilerPlugin {
-  func resolveMacro(moduleName: String, typeName: String) -> Macro.Type? {
+  @_spi(Testing)
+  public func resolveMacro(moduleName: String, typeName: String) throws -> Macro.Type {
     let qualifedName = "\(moduleName).\(typeName)"
 
     for type in providingMacros {
@@ -74,12 +75,9 @@ extension CompilerPlugin {
         return type
       }
     }
-    return nil
-  }
 
-  // @testable
-  public func _resolveMacro(moduleName: String, typeName: String) -> Macro.Type? {
-    resolveMacro(moduleName: moduleName, typeName: typeName)
+    let pluginPath = CommandLine.arguments.first ?? Bundle.main.executablePath ?? ProcessInfo.processInfo.processName
+    throw CompilerPluginError(message: "macro implementation type '\(moduleName).\(typeName)' could not be found in executable plugin '\(pluginPath)'")
   }
 }
 
@@ -88,8 +86,8 @@ struct MacroProviderAdapter<Plugin: CompilerPlugin>: PluginProvider {
   init(plugin: Plugin) {
     self.plugin = plugin
   }
-  func resolveMacro(moduleName: String, typeName: String) -> Macro.Type? {
-    plugin.resolveMacro(moduleName: moduleName, typeName: typeName)
+  func resolveMacro(moduleName: String, typeName: String) throws -> Macro.Type {
+    try plugin.resolveMacro(moduleName: moduleName, typeName: typeName)
   }
 }
 
@@ -242,3 +240,10 @@ private extension FileHandle {
     }
   }
 }
+
+struct CompilerPluginError: Error, CustomStringConvertible {
+  var description: String
+  init(message: String) {
+    self.description = message
+  }
+}
diff --git a/Sources/SwiftCompilerPluginMessageHandling/CompilerPluginMessageHandler.swift b/Sources/SwiftCompilerPluginMessageHandling/CompilerPluginMessageHandler.swift
index a7bca3ebf53..dd836a2f73c 100644
--- a/Sources/SwiftCompilerPluginMessageHandling/CompilerPluginMessageHandler.swift
+++ b/Sources/SwiftCompilerPluginMessageHandling/CompilerPluginMessageHandler.swift
@@ -20,7 +20,7 @@ public enum PluginFeature: String {
 /// A type that provides the actual plugin functions.
 public protocol PluginProvider {
   /// Resolve macro type by the module name and the type name.
-  func resolveMacro(moduleName: String, typeName: String) -> Macro.Type?
+  func resolveMacro(moduleName: String, typeName: String) throws -> Macro.Type
 
   /// Load dynamic link library at `libraryPath`. Implementations can use
   /// `moduleName` to associate the loaded library with it.
diff --git a/Sources/SwiftCompilerPluginMessageHandling/Macros.swift b/Sources/SwiftCompilerPluginMessageHandling/Macros.swift
index 5d65f8899df..1f9b13b5153 100644
--- a/Sources/SwiftCompilerPluginMessageHandling/Macros.swift
+++ b/Sources/SwiftCompilerPluginMessageHandling/Macros.swift
@@ -19,8 +19,8 @@ import SwiftSyntaxMacros
 
 extension CompilerPluginMessageHandler {
   /// Get concrete macro type from a pair of module name and type name.
-  private func resolveMacro(_ ref: PluginMessage.MacroReference) -> Macro.Type? {
-    provider.resolveMacro(moduleName: ref.moduleName, typeName: ref.typeName)
+  private func resolveMacro(_ ref: PluginMessage.MacroReference) throws -> Macro.Type {
+    try provider.resolveMacro(moduleName: ref.moduleName, typeName: ref.typeName)
   }
 
   /// Expand `@freestainding(XXX)` macros.
@@ -43,10 +43,7 @@ extension CompilerPluginMessageHandler {
       guard let macroSyntax = syntax.asProtocol(FreestandingMacroExpansionSyntax.self) else {
         throw MacroExpansionError.freestandingMacroSyntaxIsNotMacro
       }
-      guard let macroDefinition = resolveMacro(macro) else {
-        throw MacroExpansionError.macroTypeNotFound(macro)
-      }
-
+      let macroDefinition = try resolveMacro(macro)
       let macroRole: MacroRole
       if let pluginMacroRole {
         macroRole = MacroRole(messageMacroRole: pluginMacroRole)
@@ -113,9 +110,7 @@ extension CompilerPluginMessageHandler {
     // TODO: Make this a 'String?' and remove non-'hasExpandMacroResult' branches.
     let expandedSources: [String]?
     do {
-      guard let macroDefinition = resolveMacro(macro) else {
-        throw MacroExpansionError.macroTypeNotFound(macro)
-      }
+      let macroDefinition = try resolveMacro(macro)
       let role = MacroRole(messageMacroRole: macroRole)
 
       let expansions = SwiftSyntaxMacroExpansion.expandAttachedMacroWithoutCollapsing(
diff --git a/Tests/SwiftCompilerPluginTest/CompilerPluginTests.swift b/Tests/SwiftCompilerPluginTest/CompilerPluginTests.swift
index 1ccab7946c6..5a981224992 100644
--- a/Tests/SwiftCompilerPluginTest/CompilerPluginTests.swift
+++ b/Tests/SwiftCompilerPluginTest/CompilerPluginTests.swift
@@ -10,7 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import SwiftCompilerPlugin
+@_spi(Testing) import SwiftCompilerPlugin
 import SwiftSyntax
 import SwiftSyntaxMacros
 import XCTest
@@ -51,7 +51,7 @@ public class CompilerPluginTests: XCTestCase {
   func testResolveMacro() {
     let plugin = MyPlugin()
 
-    let registeredMacro = plugin._resolveMacro(
+    let registeredMacro = try? plugin.resolveMacro(
       moduleName: "SwiftCompilerPluginTest",
       typeName: "RegisteredMacro"
     )
@@ -59,12 +59,12 @@ public class CompilerPluginTests: XCTestCase {
     XCTAssertTrue(registeredMacro == RegisteredMacro.self)
 
     /// Test the plugin doesn't provide unregistered macros.
-    let dummyMacro = plugin._resolveMacro(
-      moduleName: "SwiftCompilerPluginTest",
-      typeName: "DummyMacro"
+    XCTAssertThrowsError(
+      try plugin.resolveMacro(
+        moduleName: "SwiftCompilerPluginTest",
+        typeName: "DummyMacro"
+      )
     )
-    XCTAssertNil(dummyMacro)
-    XCTAssertFalse(dummyMacro == DummyMacro.self)
 
   }
 }