#pragma clang attribute pop with no matching push

I have just upgraded a workspace from 8 to 9.1. It has a mixture of Objective-C and Swift.

I've gone through the changes to convert everything to Swift 4. The app builds and runs without error.

When I try to run the unit tests, I receive a compile error in my <module_name>-Swift.h generated file.

// Generated by Apple Swift version 4.0.2 (swiftlang-900.0.69.2 clang-900.0.38)

#pragma clang diagnostic push

#pragma clang diagnostic ignored "-Wgcc-compat"

...

#if __has_attribute(external_source_symbol)

# define SWIFT_STRINGIFY(str) #str

# define SWIFT_MODULE_NAMESPACE_PUSH(module_name) _Pragma(SWIFT_STRINGIFY(clang attribute push(__attribute__((external_source_symbol(language="Swift", defined_in=module_name, generated_declaration))), apply_to=any(function, enum, objc_interface, objc_category, objc_protocol))))

# define SWIFT_MODULE_NAMESPACE_POP _Pragma("clang attribute pop")

#else

# define SWIFT_MODULE_NAMESPACE_PUSH(module_name)

# define SWIFT_MODULE_NAMESPACE_POP

#endif

...

SWIFT_MODULE_NAMESPACE_PUSH("<module_name>")

...

SWIFT_MODULE_NAMESPACE_POP

#pragma clang diagnostic pop

The line (in bold) above returns an error message that says: '#pragma clang attribute pop' with no matching '#pragma clang attribute push'

I'm using Xcode Version 9.1 (9B55)