diff --git a/sys/src/9/pc64/dat.h b/sys/src/9/pc64/dat.h
index 8106cf1cb..0422f2b08 100644
--- a/sys/src/9/pc64/dat.h
+++ b/sys/src/9/pc64/dat.h
@@ -216,6 +216,9 @@ struct Mach
 	int	cpuiddx;
 	char	cpuidid[16];
 	char*	cpuidtype;
+	uchar	cpuidfamily;
+	uchar	cpuidmodel;
+	uchar	cpuidstepping;
 	int	havetsc;
 	int	havepge;
 	int	havewatchpt8;
diff --git a/sys/src/9/pc64/main.c b/sys/src/9/pc64/main.c
index 997322e43..fc1bfeb92 100644
--- a/sys/src/9/pc64/main.c
+++ b/sys/src/9/pc64/main.c
@@ -588,7 +588,7 @@ void
 mathinit(void)
 {
 	trapenable(VectorCERR, matherror, 0, "matherror");
-	if(X86FAMILY(m->cpuidax) == 3)
+	if(m->cpuidfamily == 3)
 		intrenable(IrqIRQ13, matherror, 0, BUSUNKNOWN, "matherror");
 	trapenable(VectorCNA, mathemu, 0, "mathemu");
 	trapenable(VectorCSO, mathover, 0, "mathover");