diff --git a/src/lj_carith.c b/src/lj_carith.c
index a7d92983..46f07be7 100644
--- a/src/lj_carith.c
+++ b/src/lj_carith.c
@@ -184,7 +184,12 @@ static int carith_int64(lua_State *L, CTState *cts, CDArith *ca, MMS mm)
       else
 	*up = u0 % u1;
       break;
-    case MM_pow: *up = lj_carith_powi64(u0, u1, (id == CTID_UINT64)); break;
+    case MM_pow:
+      if (id == CTID_INT64)
+	*up = (uint64_t)lj_carith_powi64((int64_t)u0, (int64_t)u1);
+      else
+	*up = lj_carith_powu64(u0, u1);
+      break;
     case MM_unm: *up = (uint64_t)-(int64_t)u0; break;
     default: lua_assert(0); break;
     }
@@ -225,24 +230,12 @@ int lj_carith_op(lua_State *L, MMS mm)
 
 /* -- 64 bit integer arithmetic helpers ----------------------------------- */
 
-/* 64 bit integer x^k. */
-uint64_t lj_carith_powi64(uint64_t x, uint64_t k, int isunsigned)
+/* Unsigned 64 bit x^k. */
+uint64_t lj_carith_powu64(uint64_t x, uint64_t k)
 {
-  uint64_t y = 0;
+  uint64_t y;
   if (k == 0)
     return 1;
-  if (!isunsigned) {
-    if ((int64_t)k < 0) {
-      if (x == 0)
-	return U64x(7fffffff,ffffffff);
-      else if (x == 1)
-	return 1;
-      else if ((int64_t)x == -1)
-	return (k & 1) ? -1 : 1;
-      else
-	return 0;
-    }
-  }
   for (; (k & 1) == 0; k >>= 1) x *= x;
   y = x;
   if ((k >>= 1) != 0) {
@@ -257,4 +250,22 @@ uint64_t lj_carith_powi64(uint64_t x, uint64_t k, int isunsigned)
   return y;
 }
 
+/* Signed 64 bit x^k. */
+int64_t lj_carith_powi64(int64_t x, int64_t k)
+{
+  if (k == 0)
+    return 1;
+  if (k < 0) {
+    if (x == 0)
+      return U64x(7fffffff,ffffffff);
+    else if (x == 1)
+      return 1;
+    else if (x == -1)
+      return (k & 1) ? -1 : 1;
+    else
+      return 0;
+  }
+  return (int64_t)lj_carith_powu64((uint64_t)x, (uint64_t)k);
+}
+
 #endif
diff --git a/src/lj_carith.h b/src/lj_carith.h
index acb095db..6870172b 100644
--- a/src/lj_carith.h
+++ b/src/lj_carith.h
@@ -12,7 +12,8 @@
 
 LJ_FUNC int lj_carith_op(lua_State *L, MMS mm);
 
-LJ_FUNC uint64_t lj_carith_powi64(uint64_t x, uint64_t k, int isunsigned);
+LJ_FUNC uint64_t lj_carith_powu64(uint64_t x, uint64_t k);
+LJ_FUNC int64_t lj_carith_powi64(int64_t x, int64_t k);
 
 #endif
 
diff --git a/src/lj_crecord.c b/src/lj_crecord.c
index 647c464a..86e95679 100644
--- a/src/lj_crecord.c
+++ b/src/lj_crecord.c
@@ -689,8 +689,8 @@ static TRef crec_arith_int64(jit_State *J, TRef *sp, CType **s, MMS mm)
       J->postproc = LJ_POST_FIXGUARD;
       return TREF_TRUE;
     } else if (mm == MM_pow) {
-      tr = lj_ir_call(J, IRCALL_lj_carith_powi64, sp[0], sp[1],
-		      lj_ir_kint(J, (int)dt-(int)IRT_I64));
+      tr = lj_ir_call(J, dt == IRT_I64 ? IRCALL_lj_carith_powi64 :
+					 IRCALL_lj_carith_powu64, sp[0], sp[1]);
     } else {
       if (mm == MM_div || mm == MM_mod)
 	return 0;  /* NYI: integer div, mod. */
diff --git a/src/lj_ir.h b/src/lj_ir.h
index 6dee36c6..1cb3566e 100644
--- a/src/lj_ir.h
+++ b/src/lj_ir.h
@@ -251,11 +251,13 @@ typedef struct CCallInfo {
 #define CCI_CASTU64		0x0200	/* Cast u64 result to number. */
 #define CCI_NOFPRCLOBBER	0x0400	/* Does not clobber any FPRs. */
 #define CCI_FASTCALL		0x0800	/* Fastcall convention. */
+#define CCI_STACK64		0x1000	/* Needs 64 bits per argument. */
 
 /* Function definitions for CALL* instructions. */
 #if LJ_HASFFI
 #define IRCALLDEF_FFI(_) \
-  _(lj_carith_powi64,	3,   N, U64, CCI_NOFPRCLOBBER)
+  _(lj_carith_powi64,	2,   N, I64, CCI_STACK64|CCI_NOFPRCLOBBER) \
+  _(lj_carith_powu64,	2,   N, U64, CCI_STACK64|CCI_NOFPRCLOBBER)
 #else
 #define IRCALLDEF_FFI(_)
 #endif