diff --git a/applications/test/pTraits/Make/files b/applications/test/pTraits/Make/files
index 268e879af2..df4c770c13 100644
--- a/applications/test/pTraits/Make/files
+++ b/applications/test/pTraits/Make/files
@@ -1,2 +1,3 @@
-Test-pTraits.C
+Test-pTraits.cxx
+
 EXE = $(FOAM_USER_APPBIN)/Test-pTraits
diff --git a/applications/test/pTraits/Test-pTraits.C b/applications/test/pTraits/Test-pTraits.cxx
similarity index 100%
rename from applications/test/pTraits/Test-pTraits.C
rename to applications/test/pTraits/Test-pTraits.cxx
diff --git a/src/OpenFOAM/primitives/ints/int64/int64.H b/src/OpenFOAM/primitives/ints/int64/int64.H
index e88716e14a..33478848b0 100644
--- a/src/OpenFOAM/primitives/ints/int64/int64.H
+++ b/src/OpenFOAM/primitives/ints/int64/int64.H
@@ -126,7 +126,7 @@ Ostream& operator<<(Ostream& os, const int64_t val);
 // On Darwin:
 // long is not unambiguously (int32_t | int64_t)
 // - explicitly resolve for input and output
-#if defined(__APPLE__)
+#ifdef __APPLE__
     Istream& operator>>(Istream& is, long& val);
     Ostream& operator<<(Ostream& os, const long val);
 #endif
@@ -196,6 +196,11 @@ public:
 };
 
 
+#ifdef __APPLE__
+//- On Darwin: long is not unambiguously (int64_t)
+template<> class pTraits<long> : pTraits<int64_t> {};
+#endif
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace Foam
diff --git a/src/OpenFOAM/primitives/ints/int64/int64IO.C b/src/OpenFOAM/primitives/ints/int64/int64IO.C
index 93f73585ce..ed4136d7f5 100644
--- a/src/OpenFOAM/primitives/ints/int64/int64IO.C
+++ b/src/OpenFOAM/primitives/ints/int64/int64IO.C
@@ -182,7 +182,7 @@ Foam::Ostream& Foam::operator<<(Ostream& os, const int64_t val)
 }
 
 
-#if defined(__APPLE__)
+#ifdef __APPLE__
 Foam::Istream& Foam::operator>>(Istream& is, long& val)
 {
     return operator>>(is, reinterpret_cast<int64_t&>(val));
diff --git a/src/OpenFOAM/primitives/ints/uint64/uint64.H b/src/OpenFOAM/primitives/ints/uint64/uint64.H
index 3c352e4148..6caac03855 100644
--- a/src/OpenFOAM/primitives/ints/uint64/uint64.H
+++ b/src/OpenFOAM/primitives/ints/uint64/uint64.H
@@ -186,6 +186,11 @@ public:
 };
 
 
+#ifdef __APPLE__
+//- On Darwin: unsigned long is not unambiguously (uint64_t)
+template<> class pTraits<unsigned long> : pTraits<uint64_t> {};
+#endif
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace Foam