diff --git a/Sources/ProjectSpec/SpecValidation.swift b/Sources/ProjectSpec/SpecValidation.swift
index fa7d2add..5967e79b 100644
--- a/Sources/ProjectSpec/SpecValidation.swift
+++ b/Sources/ProjectSpec/SpecValidation.swift
@@ -156,6 +156,10 @@ extension Project {
                             errors.append(.invalidSDKDependency(target: target.name, dependency: dependency.reference))
                         }
                     }
+                case .package:
+                    if packages[dependency.reference] == nil {
+                        errors.append(.invalidSwiftPackage(name: dependency.reference, target: target.name))
+                    }
                 default: break
                 }
             }
diff --git a/Sources/ProjectSpec/SpecValidationError.swift b/Sources/ProjectSpec/SpecValidationError.swift
index d1a7a0b0..d1cdf0c9 100644
--- a/Sources/ProjectSpec/SpecValidationError.swift
+++ b/Sources/ProjectSpec/SpecValidationError.swift
@@ -18,6 +18,7 @@ public struct SpecValidationError: Error, CustomStringConvertible {
         case invalidTargetSchemeTest(target: String, testTarget: String)
         case invalidSchemeTarget(scheme: String, target: String)
         case invalidSchemeConfig(scheme: String, config: String)
+        case invalidSwiftPackage(name: String, target: String)
         case invalidConfigFile(configFile: String, config: String)
         case invalidBuildSettingConfig(String)
         case invalidSettingsGroup(String)
@@ -61,6 +62,8 @@ public struct SpecValidationError: Error, CustomStringConvertible {
                 return "Invalid file group \(group.quoted)"
             case let .invalidConfigFileConfig(config):
                 return "Config file has invalid config \(config.quoted)"
+            case let .invalidSwiftPackage(name, target):
+                return "Target \(target.quoted) has an invalid package dependency \(name.quoted)"
             case let .missingConfigForTargetScheme(target, configType):
                 return "Target \(target.quoted) is missing a config of type \(configType.rawValue) to generate its scheme"
             case let .missingDefaultConfig(name):
diff --git a/Tests/XcodeGenKitTests/ProjectSpecTests.swift b/Tests/XcodeGenKitTests/ProjectSpecTests.swift
index 346ba865..8860f8e1 100644
--- a/Tests/XcodeGenKitTests/ProjectSpecTests.swift
+++ b/Tests/XcodeGenKitTests/ProjectSpecTests.swift
@@ -134,7 +134,10 @@ class ProjectSpecTests: XCTestCase {
                     settings: invalidSettings,
                     configFiles: ["invalidConfig": "invalidConfigFile"],
                     sources: ["invalidSource"],
-                    dependencies: [Dependency(type: .target, reference: "invalidDependency")],
+                    dependencies: [
+                        Dependency(type: .target, reference: "invalidDependency"),
+                        Dependency(type: .package(product: nil), reference: "invalidPackage")
+                    ],
                     preBuildScripts: [BuildScript(script: .path("invalidPreBuildScript"), name: "preBuildScript1")],
                     postCompileScripts: [BuildScript(script: .path("invalidPostCompileScript"))],
                     postBuildScripts: [BuildScript(script: .path("invalidPostBuildScript"))],
@@ -142,6 +145,7 @@ class ProjectSpecTests: XCTestCase {
                 )]
 
                 try expectValidationError(project, .invalidTargetDependency(target: "target1", dependency: "invalidDependency"))
+                try expectValidationError(project, .invalidSwiftPackage(name: "invalidPackage", target: "target1"))
                 try expectValidationError(project, .invalidTargetConfigFile(target: "target1", configFile: "invalidConfigFile", config: "invalidConfig"))
                 try expectValidationError(project, .invalidTargetSchemeTest(target: "target1", testTarget: "invalidTarget"))
                 try expectValidationError(project, .invalidTargetSource(target: "target1", source: "invalidSource"))