diff --git a/src/runtime/asm_ppc64x.s b/src/runtime/asm_ppc64x.s
index e77c717935..87076817f9 100644
--- a/src/runtime/asm_ppc64x.s
+++ b/src/runtime/asm_ppc64x.s
@@ -648,7 +648,7 @@ TEXT ·cgocallback_gofunc(SB),NOSPLIT,$16-32
 	NO_LOCAL_POINTERS
 
 	// Load m and g from thread-local storage.
-	MOVB	runtime·iscgo(SB), R3
+	MOVBZ	runtime·iscgo(SB), R3
 	CMP	R3, $0
 	BEQ	nocgo
 	BL	runtime·load_g(SB)
diff --git a/src/runtime/sys_linux_ppc64x.s b/src/runtime/sys_linux_ppc64x.s
index 5b5df50d41..bf01099830 100644
--- a/src/runtime/sys_linux_ppc64x.s
+++ b/src/runtime/sys_linux_ppc64x.s
@@ -301,7 +301,7 @@ TEXT runtime·_sigtramp(SB),NOSPLIT,$64
 
 	// this might be called in external code context,
 	// where g is not set.
-	MOVB	runtime·iscgo(SB), R6
+	MOVBZ	runtime·iscgo(SB), R6
 	CMP 	R6, $0
 	BEQ	2(PC)
 	BL	runtime·load_g(SB)
diff --git a/src/runtime/tls_ppc64x.s b/src/runtime/tls_ppc64x.s
index 82714853ee..c697449282 100644
--- a/src/runtime/tls_ppc64x.s
+++ b/src/runtime/tls_ppc64x.s
@@ -24,7 +24,7 @@
 // NOTE: setg_gcc<> assume this clobbers only R31.
 TEXT runtime·save_g(SB),NOSPLIT|NOFRAME,$0-0
 #ifndef GOOS_aix
-	MOVB	runtime·iscgo(SB), R31
+	MOVBZ	runtime·iscgo(SB), R31
 	CMP	R31, $0
 	BEQ	nocgo
 #endif