diff --git a/pc-bios/s390-ccw/helper.h b/pc-bios/s390-ccw/helper.h
index dfcfea0ff0..3d0731c4c6 100644
--- a/pc-bios/s390-ccw/helper.h
+++ b/pc-bios/s390-ccw/helper.h
@@ -31,7 +31,7 @@ static inline void *u32toptr(uint32_t n)
 
 static inline void yield(void)
 {
-    asm volatile ("diag 0,0,0x44"
+    asm volatile ("diag %%r0,%%r0,0x44"
                   : :
                   : "memory", "cc");
 }
diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
index 73e4367e09..78f5f46533 100644
--- a/pc-bios/s390-ccw/jump2ipl.c
+++ b/pc-bios/s390-ccw/jump2ipl.c
@@ -64,8 +64,8 @@ void jump_to_IPL_code(uint64_t address)
      * We use the load normal reset to keep r15 unchanged. jump_to_IPL_2
      * can then use r15 as its stack pointer.
      */
-    asm volatile("lghi 1,1\n\t"
-                 "diag 1,1,0x308\n\t"
+    asm volatile("lghi %%r1,1\n\t"
+                 "diag %%r1,%%r1,0x308\n\t"
                  : : : "1", "memory");
     panic("\n! IPL returns !\n");
 }
diff --git a/pc-bios/s390-ccw/menu.c b/pc-bios/s390-ccw/menu.c
index de8260a5d6..d601952d3e 100644
--- a/pc-bios/s390-ccw/menu.c
+++ b/pc-bios/s390-ccw/menu.c
@@ -36,9 +36,9 @@ static inline void enable_clock_int(void)
     uint64_t tmp = 0;
 
     asm volatile(
-        "stctg      0,0,%0\n"
+        "stctg      %%c0,%%c0,%0\n"
         "oi         6+%0, 0x8\n"
-        "lctlg      0,0,%0"
+        "lctlg      %%c0,%%c0,%0"
         : : "Q" (tmp) : "memory"
     );
 }
@@ -48,9 +48,9 @@ static inline void disable_clock_int(void)
     uint64_t tmp = 0;
 
     asm volatile(
-        "stctg      0,0,%0\n"
+        "stctg      %%c0,%%c0,%0\n"
         "ni         6+%0, 0xf7\n"
-        "lctlg      0,0,%0"
+        "lctlg      %%c0,%%c0,%0"
         : : "Q" (tmp) : "memory"
     );
 }
diff --git a/pc-bios/s390-ccw/virtio.c b/pc-bios/s390-ccw/virtio.c
index ab49840db8..5d2c6e3381 100644
--- a/pc-bios/s390-ccw/virtio.c
+++ b/pc-bios/s390-ccw/virtio.c
@@ -54,7 +54,7 @@ static long kvm_hypercall(unsigned long nr, unsigned long param1,
     register ulong r_param3 asm("4") = param3;
     register long retval asm("2");
 
-    asm volatile ("diag 2,4,0x500"
+    asm volatile ("diag %%r2,%%r4,0x500"
                   : "=d" (retval)
                   : "d" (r_nr), "0" (r_param1), "r"(r_param2), "d"(r_param3)
                   : "memory", "cc");