diff --git a/dynasm/dasm_x86.h b/dynasm/dasm_x86.h
index 2e2f2334..d8d4928c 100644
--- a/dynasm/dasm_x86.h
+++ b/dynasm/dasm_x86.h
@@ -239,8 +239,11 @@ void dasm_put(Dst_DECL, int start, ...)
 	}
 	pos++;
 	ofs += 4;  /* Maximum offset needed. */
-	if (action == DASM_REL_LG || action == DASM_REL_PC)
+	if (action == DASM_REL_LG || action == DASM_REL_PC) {
 	  b[pos++] = ofs;  /* Store pass1 offset estimate. */
+	} else if (sizeof(ptrdiff_t) == 8) {
+	  ofs += 4;
+	}
 	break;
       case DASM_LABEL_LG: pl = D->lglabels + *p++; CKPL(lg, LG); goto putlabel;
       case DASM_LABEL_PC: pl = D->pclabels + va_arg(ap, int); CKPL(pc, PC);
@@ -365,10 +368,22 @@ int dasm_link(Dst_DECL, size_t *szp)
   do { *((unsigned short *)cp) = (unsigned short)(x); cp+=2; } while (0)
 #define dasmd(x) \
   do { *((unsigned int *)cp) = (unsigned int)(x); cp+=4; } while (0)
+#define dasmq(x) \
+  do { *((unsigned long long *)cp) = (unsigned long long)(x); cp+=8; } while (0)
 #else
 #define dasmw(x)	do { dasmb(x); dasmb((x)>>8); } while (0)
 #define dasmd(x)	do { dasmw(x); dasmw((x)>>16); } while (0)
+#define dasmq(x)	do { dasmd(x); dasmd((x)>>32); } while (0)
 #endif
+static unsigned char *dasma_(unsigned char *cp, ptrdiff_t x)
+{
+  if (sizeof(ptrdiff_t) == 8)
+    dasmq((unsigned long long)x);
+  else
+    dasmd((unsigned int)x);
+  return cp;
+}
+#define dasma(x)	(cp = dasma_(cp, (x)))
 
 /* Pass 3: Encode sections. */
 int dasm_encode(Dst_DECL, void *buffer)
@@ -443,12 +458,13 @@ int dasm_encode(Dst_DECL, void *buffer)
 	  goto wb;
 	}
 	case DASM_IMM_LG:
-	  p++; if (n < 0) { n = (int)(ptrdiff_t)D->globals[-n]; goto wd; }
+	  p++;
+	  if (n < 0) { dasma((ptrdiff_t)D->globals[-n]); break; }
 	  /* fallthrough */
 	case DASM_IMM_PC: {
 	  int *pb = DASM_POS2PTR(D, n);
-	  n = *pb < 0 ? pb[1] : (*pb + (int)(ptrdiff_t)base);
-	  goto wd;
+	  dasma(*pb < 0 ? (ptrdiff_t)pb[1] : (*pb + (ptrdiff_t)base));
+	  break;
 	}
 	case DASM_LABEL_LG: {
 	  int idx = *p++;
diff --git a/dynasm/dasm_x86.lua b/dynasm/dasm_x86.lua
index bc9a0001..0c803dcd 100644
--- a/dynasm/dasm_x86.lua
+++ b/dynasm/dasm_x86.lua
@@ -484,6 +484,22 @@ local function wputdarg(n)
   end
 end
 
+-- Put signed or unsigned qword or arg.
+local function wputqarg(n)
+  local tn = type(n)
+  if tn == "number" then -- This is only used for numbers from -2^31..2^32-1.
+    wputb(band(n, 255))
+    wputb(band(shr(n, 8), 255))
+    wputb(band(shr(n, 16), 255))
+    wputb(shr(n, 24))
+    local sign = n < 0 and 255 or 0
+    wputb(sign); wputb(sign); wputb(sign); wputb(sign)
+  else
+    waction("IMM_D", format("(unsigned int)(%s)", n))
+    waction("IMM_D", format("(unsigned int)((unsigned long long)(%s)>>32)", n))
+  end
+end
+
 -- Put operand-size dependent number or arg (defaults to dword).
 local function wputszarg(sz, n)
   if not sz or sz == "d" or sz == "q" then wputdarg(n)
@@ -663,10 +679,16 @@ local function opmodestr(op, args)
 end
 
 -- Convert number to valid integer or nil.
-local function toint(expr)
+local function toint(expr, isqword)
   local n = tonumber(expr)
   if n then
-    if n % 1 ~= 0 or n < -2147483648 or n > 4294967295 then
+    if n % 1 ~= 0 then
+      werror("not an integer number `"..expr.."'")
+    elseif isqword then
+      if n < -2147483648 or n > 2147483647 then
+	n = nil -- Handle it as an expression to avoid precision loss.
+      end
+    elseif n < -2147483648 or n > 4294967295 then
       werror("bad integer number `"..expr.."'")
     end
     return n
@@ -749,7 +771,7 @@ local function rtexpr(expr)
 end
 
 -- Parse operand and return { mode, opsize, reg, xreg, xsc, disp, imm }.
-local function parseoperand(param)
+local function parseoperand(param, isqword)
   local t = {}
 
   local expr = param
@@ -837,7 +859,7 @@ local function parseoperand(param)
       t.disp = dispexpr(tailx)
     else
       -- imm or opsize*imm
-      local imm = toint(expr)
+      local imm = toint(expr, isqword)
       if not imm and sub(expr, 1, 1) == "*" and t.opsize then
 	imm = toint(sub(expr, 2))
 	if imm then
@@ -1952,7 +1974,7 @@ local function dopattern(pat, args, sz, op, needrex)
 	local a = args[narg]
 	narg = narg + 1
 	local mode, imm = a.mode, a.imm
-	if mode == "iJ" and not match("iIJ", c) then
+	if mode == "iJ" and not match(x64 and "J" or "iIJ", c) then
 	  werror("bad operand size for label")
 	end
 	if c == "S" then
@@ -2144,14 +2166,16 @@ end
 local function op_data(params)
   if not params then return "imm..." end
   local sz = sub(params.op, 2, 2)
-  if sz == "a" then sz = addrsize end
+  if sz == "l" then sz = "d" elseif sz == "a" then sz = addrsize end
   for _,p in ipairs(params) do
-    local a = parseoperand(p)
+    local a = parseoperand(p, sz == "q")
     if sub(a.mode, 1, 1) ~= "i" or (a.opsize and a.opsize ~= sz) then
       werror("bad mode or size in `"..p.."'")
     end
     if a.mode == "iJ" then
       wputlabel("IMM_", a.imm, 1)
+    elseif sz == "q" then
+      wputqarg(a.imm)
     else
       wputszarg(sz, a.imm)
     end
@@ -2163,7 +2187,11 @@ map_op[".byte_*"] = op_data
 map_op[".sbyte_*"] = op_data
 map_op[".word_*"] = op_data
 map_op[".dword_*"] = op_data
+map_op[".qword_*"] = op_data
 map_op[".aword_*"] = op_data
+map_op[".long_*"] = op_data
+map_op[".quad_*"] = op_data
+map_op[".addr_*"] = op_data
 
 ------------------------------------------------------------------------------