diff --git a/LEGO1/omni/include/mxatom.h b/LEGO1/omni/include/mxatom.h
index 5a4b6877..9528a3c6 100644
--- a/LEGO1/omni/include/mxatom.h
+++ b/LEGO1/omni/include/mxatom.h
@@ -68,6 +68,12 @@ class MxAtomId {
 	// FUNCTION: BETA10 0x100178d0
 	inline MxBool operator==(const MxAtomId& p_atomId) const { return this->m_internal == p_atomId.m_internal; }
 
+#ifdef COMPAT_MODE
+	// Required for modern compilers.
+	// MSVC 4.20 uses a synthetic function from INCLUDE/UTILITY that inverts operator==
+	inline MxBool operator!=(const MxAtomId& p_atomId) const { return this->m_internal != p_atomId.m_internal; }
+#endif
+
 	// FUNCTION: BETA10 0x10025d40
 	MxAtomId() { this->m_internal = 0; }