diff --git a/Sources/protoc-gen-swift/FileGenerator.swift b/Sources/protoc-gen-swift/FileGenerator.swift
index 3aa749359..90fd06a69 100644
--- a/Sources/protoc-gen-swift/FileGenerator.swift
+++ b/Sources/protoc-gen-swift/FileGenerator.swift
@@ -91,6 +91,15 @@ class FileGenerator {
 
         p.print("import Foundation\n")
 
+        if self.generatorOptions.implementationOnlyImports,
+           self.generatorOptions.visibility == .public {
+            errorString = """
+                Cannot use @_implementationOnly imports when the proto visibility is public.
+                Either change the visibility to internal, or disable @_implementationOnly imports.
+            """
+            return
+        }
+
         // Import all other imports as @_implementationOnly if the visiblity is
         // internal and the option is set, to avoid exposing internal types to users.
         let visibilityAnnotation: String = {