diff --git a/dynasm/dasm_x86.h b/dynasm/dasm_x86.h
index 2e2f2334..9a1d8b54 100644
--- a/dynasm/dasm_x86.h
+++ b/dynasm/dasm_x86.h
@@ -17,11 +17,11 @@
 
 /* Action definitions. DASM_STOP must be 255. */
 enum {
-  DASM_DISP = 233,
+  DASM_DISP = 231,
   DASM_IMM_S, DASM_IMM_B, DASM_IMM_W, DASM_IMM_D, DASM_IMM_WB, DASM_IMM_DB,
   DASM_VREG, DASM_SPACE, DASM_SETLABEL, DASM_REL_A, DASM_REL_LG, DASM_REL_PC,
-  DASM_IMM_LG, DASM_IMM_PC, DASM_LABEL_LG, DASM_LABEL_PC, DASM_ALIGN,
-  DASM_EXTERN, DASM_ESC, DASM_MARK, DASM_SECTION, DASM_STOP
+  DASM_IMM_LG, DASM_IMM_LG64, DASM_IMM_PC, DASM_IMM_PC64, DASM_LABEL_LG, DASM_LABEL_PC,
+  DASM_ALIGN, DASM_EXTERN, DASM_ESC, DASM_MARK, DASM_SECTION, DASM_STOP
 };
 
 /* Maximum number of section buffer positions for a single dasm_put() call. */
@@ -218,6 +218,7 @@ void dasm_put(Dst_DECL, int start, ...)
     } else {
       int *pl, n;
       switch (action) {
+      case DASM_IMM_LG64: ofs += 4;
       case DASM_REL_LG:
       case DASM_IMM_LG:
 	n = *p++; pl = D->lglabels + n;
@@ -226,6 +227,7 @@ void dasm_put(Dst_DECL, int start, ...)
 	pl -= 246; n = *pl;
 	if (n < 0) n = 0;  /* Start new chain for fwd rel if label exists. */
 	goto linkrel;
+	  case DASM_IMM_PC64: ofs += 4;
       case DASM_REL_PC:
       case DASM_IMM_PC: pl = D->pclabels + va_arg(ap, int); CKPL(pc, PC);
       putrel:
@@ -333,11 +335,12 @@ int dasm_link(Dst_DECL, size_t *szp)
 	  break;
 	}
 	  /* fallthrough */
-	case DASM_SPACE: case DASM_IMM_LG: case DASM_VREG: p++;
+	case DASM_SPACE: case DASM_IMM_LG: case DASM_IMM_LG64: case DASM_VREG: p++;
 	  /* fallthrough */
 	case DASM_DISP: case DASM_IMM_S: case DASM_IMM_B: case DASM_IMM_W:
 	case DASM_IMM_D: case DASM_IMM_WB: case DASM_IMM_DB:
-	case DASM_SETLABEL: case DASM_REL_A: case DASM_IMM_PC: pos++; break;
+	case DASM_SETLABEL: case DASM_REL_A: case DASM_IMM_PC: case DASM_IMM_PC64:
+	  pos++; break;
 	case DASM_LABEL_LG: p++;
 	  /* fallthrough */
 	case DASM_LABEL_PC: b[pos++] += ofs; break; /* Fix label offset. */
@@ -365,9 +368,12 @@ 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 { *((uint64_t *)cp) = (uint64_t)(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
 
 /* Pass 3: Encode sections. */
@@ -450,6 +456,16 @@ int dasm_encode(Dst_DECL, void *buffer)
 	  n = *pb < 0 ? pb[1] : (*pb + (int)(ptrdiff_t)base);
 	  goto wd;
 	}
+	case DASM_IMM_LG64: {
+	  p++;
+	  if (n < 0)
+	    dasmq((ptrdiff_t)D->globals[-n]);
+	}
+	case DASM_IMM_PC64: {
+	  int *pb = DASM_POS2PTR(D, n);
+	  dasmq(*pb < 0 ? pb[1] : (*pb + (ptrdiff_t)base));
+	  break;
+	}
 	case DASM_LABEL_LG: {
 	  int idx = *p++;
 	  if (idx >= 10)
diff --git a/dynasm/dasm_x86.lua b/dynasm/dasm_x86.lua
index bc9a0001..659db2d0 100644
--- a/dynasm/dasm_x86.lua
+++ b/dynasm/dasm_x86.lua
@@ -46,8 +46,8 @@ local action_names = {
   "SETLABEL", "REL_A",
   -- action arg (1 byte) or int arg, 2 buffer pos (link, offset):
   "REL_LG", "REL_PC",
-  -- action arg (1 byte) or int arg, 1 buffer pos (link):
-  "IMM_LG", "IMM_PC",
+  -- action arg (1 byte) or ptrdiff_t arg, 1 buffer pos (link):
+  "IMM_LG", "IMM_LG64", "IMM_PC", "IMM_PC64",
   -- action arg (1 byte) or int arg, 1 buffer pos (offset):
   "LABEL_LG", "LABEL_PC",
   -- action arg (1 byte), 1 buffer pos (offset):
@@ -438,6 +438,16 @@ local function wputlabel(aprefix, imm, num)
   end
 end
 
+-- Put action for label arg (IMM_LG64, IMM_PC64, REL_LG, REL_PC).
+local function wputlabel64(aprefix, imm, num)
+  if type(imm) == "number" then
+    waction("IMM_LG64", nil, num);
+    wputxb(imm)
+  else
+    waction("IMM_PC64", imm, num)
+  end
+end
+
 -- Put signed byte or arg.
 local function wputsbarg(n)
   if type(n) == "number" then
@@ -469,6 +479,26 @@ local function wputwarg(n)
   else waction("IMM_W", n) end
 end
 
+-- Put signed or unsigned qword or arg.
+local function wputqarg(n)
+  local tn = type(n)
+  if tn == "number" then
+    wputb(band(n, 255))
+    wputb(band(shr(n, 8), 255))
+    wputb(band(shr(n, 16), 255))
+    wputb(band(shr(n, 24), 255))
+    wputb(band(shr(n, 32), 255))
+    wputb(band(shr(n, 40), 255))
+    wputb(band(shr(n, 48), 255))
+    wputb(shr(n, 56))
+  elseif tn == "table" then
+    wputlabel64("IMM_", n[1], 1)
+  else
+    waction("IMM_D", format("(unsigned int)(%s)", n))
+    waction("IMM_D", format("(unsigned int)((%s)>>32)", n))
+  end
+end
+
 -- Put signed or unsigned dword or arg.
 local function wputdarg(n)
   local tn = type(n)
@@ -2151,9 +2181,17 @@ local function op_data(params)
       werror("bad mode or size in `"..p.."'")
     end
     if a.mode == "iJ" then
-      wputlabel("IMM_", a.imm, 1)
+      if sz == 'q' then
+        wputlabel64("IMM_", a.imm, 1)
+      else
+        wputlabel("IMM_", a.imm, 1)
+      end
     else
-      wputszarg(sz, a.imm)
+      if sz == 'q' then
+        wputqarg(a.imm)
+      else
+        wputszarg(sz, a.imm)
+      end
     end
     if secpos+2 > maxsecpos then wflush() end
   end