diff --git a/src/lj_ccall.c b/src/lj_ccall.c
index a6b0a8fd..00c1c7cf 100644
--- a/src/lj_ccall.c
+++ b/src/lj_ccall.c
@@ -585,9 +585,9 @@
 
 #define CCALL_HANDLE_REGARG \
   if (isfp) { \
-    if (nfpr < maxgpr) { dp = &cc->fpr[nfpr++]; goto done; } \
+    if (nfpr < CCALL_NARG_FPR) { dp = &cc->fpr[nfpr++]; goto done; } \
   } else { \
-    if (ngpr < CCALL_NARG_FPR) { dp = &cc->gpr[ngpr++]; goto done; } \
+    if (ngpr < maxgpr) { dp = &cc->gpr[ngpr++]; goto done; } \
   }
 
 #else
@@ -1074,6 +1074,15 @@ static int ccall_set_args(lua_State *L, CTState *cts, CType *ct,
       *(int64_t *)dp = (int64_t)*(int32_t *)dp;  /* Sign-extend to 64 bit. */
     }
 #endif
+#if LJ_TARGET_S390X
+    /* Arguments need to be sign-/zero-extended to 64-bits. */
+    if ((ctype_isinteger_or_bool(d->info) || ctype_isenum(d->info)) && d->size <= 4) {
+      if (d->info & CTF_UNSIGNED)
+        *(uint64_t *)dp = (uint64_t)*(uint32_t *)dp;
+      else
+        *(int64_t *)dp = (int64_t)*(int32_t *)dp;
+    }
+#endif
 #if LJ_TARGET_X64 && LJ_ABI_WIN
     if (isva) {  /* Windows/x64 mirrors varargs in both register sets. */
       if (nfpr == ngpr)
diff --git a/src/vm_s390x.dasc b/src/vm_s390x.dasc
index f8be2847..f0289de6 100644
--- a/src/vm_s390x.dasc
+++ b/src/vm_s390x.dasc
@@ -2164,21 +2164,22 @@ static void build_subroutines(BuildCtx *ctx)
   |  basr r14, r7
   |
   |  stg CRET1, CCSTATE->gpr[0]
-  |  stg f0, CCSTATE->fpr[0]
+  |  std f0, CCSTATE->fpr[0]
   |
   |  agf sp, CCSTATE->spadj
   |  lmg r6, r15, 48(sp)
   |  br r14
   |
   |2:
+  |  sll r1, 3
   |  lay r10, (offsetof(CCallState, stack))(CCSTATE)	// Source.
   |  lay r11, (CCALL_SPS_EXTRA*8)(sp)			// Destination.
   |3:
   |  chi r1, 256
   |  jl >4
   |  mvc 0(256, r11), 0(r10)
-  |  la r10, 256*8(r10)
-  |  la r11, 256*8(r11)
+  |  la r10, 256(r10)
+  |  la r11, 256(r11)
   |  ahi r1, -256
   |  j <3
   |