diff --git a/src/cnglob.h b/src/cnglob.h
index 94140f00b..d438173ea 100644
--- a/src/cnglob.h
+++ b/src/cnglob.h
@@ -411,7 +411,7 @@ template<typename T> inline NANDAT AsNANDAT(T& v) { return *reinterpret_cast<con
 
 #define NCNAN 0x7f80		// bits that make nchoice a nan; is combined with choice index 1-7f to form stored value
 // macro to test if n has an NCHOICE value:
-#define ISNCHOICE(n)  ((AsNANDAT(n) & 0xff800000L)==0x7f800000L)
+#define ISNCHOICE(n)  ((AsNANDAT(n) & 0xff800000L)==0x7f800000L) && ((AsNANDAT(n) & 0x7FFFFFL) != 0x400000L)
 // macro to generate 32-bit value from 16-bit choice constants, for use where full value needed, as in initialized data
 //   usage:  float y = NCHOICE(C_ABCNC_X);
 #define NCHOICE(nck)  (NANDAT(static_cast<uint32_t>(nck) << 16))	// put in hi word. nck must include 0x7f80.