diff --git a/ghc/compiler/prelude/PrimOp.lhs b/ghc/compiler/prelude/PrimOp.lhs
index 305c6f76f61539e6273a9034bf3d62edb876242e..7be5595a5484827cdda81c4033810014c214de3c 100644
--- a/ghc/compiler/prelude/PrimOp.lhs
+++ b/ghc/compiler/prelude/PrimOp.lhs
@@ -157,7 +157,7 @@ data PrimOp
     | IndexOffForeignObjOp PrimRep
 
     | UnsafeFreezeArrayOp | UnsafeFreezeByteArrayOp
-    | UnsafeThawArrayOp   | UnsafeThawByteArrayOp
+    | UnsafeThawArrayOp
     | SizeofByteArrayOp   | SizeofMutableByteArrayOp
 
     -- Mutable variables
@@ -512,7 +512,6 @@ tagOf_PrimOp (WriteOffAddrOp Word64Rep)       = ILIT(200)
 tagOf_PrimOp UnsafeFreezeArrayOp	      = ILIT(201)
 tagOf_PrimOp UnsafeFreezeByteArrayOp	      = ILIT(202)
 tagOf_PrimOp UnsafeThawArrayOp		      = ILIT(203)
-tagOf_PrimOp UnsafeThawByteArrayOp	      = ILIT(204)
 tagOf_PrimOp SizeofByteArrayOp		      = ILIT(205)
 tagOf_PrimOp SizeofMutableByteArrayOp	      = ILIT(206)
 tagOf_PrimOp NewMVarOp			      = ILIT(207)
@@ -787,7 +786,6 @@ allThePrimOps
 	UnsafeFreezeArrayOp,
 	UnsafeFreezeByteArrayOp,
 	UnsafeThawArrayOp,
-	UnsafeThawByteArrayOp,
 	SizeofByteArrayOp,
 	SizeofMutableByteArrayOp,
 	NewMutVarOp,
@@ -1380,7 +1378,6 @@ primOpInfo (WriteOffAddrOp kind)
 unsafeFreezeArray#     :: MutArr# s a -> State# s -> (# State# s, Array# a #)
 unsafeFreezeByteArray# :: MutByteArr# s -> State# s -> (# State# s, ByteArray# #)
 unsafeThawArray#       :: Array# a -> State# s -> (# State# s, MutArr# s a #)
-unsafeThawByteArray#   :: ByteArray# -> State# s -> (# State# s, MutByteArr# s #)
 -}
 
 primOpInfo UnsafeFreezeArrayOp
@@ -1410,15 +1407,6 @@ primOpInfo UnsafeThawArrayOp
 	[mkArrayPrimTy elt, state]
 	(unboxedPair [state, mkMutableArrayPrimTy s elt])
 
-primOpInfo UnsafeThawByteArrayOp
-  = let { 
-	s = alphaTy; s_tv = alphaTyVar;
-	state = mkStatePrimTy s
-    } in
-    mkGenPrimOp SLIT("unsafeThawByteArray#") [s_tv]
-	[byteArrayPrimTy, state]
-	(unboxedPair [state, mkMutableByteArrayPrimTy s])
-
 ---------------------------------------------------------------------------
 primOpInfo SizeofByteArrayOp
   = mkGenPrimOp
@@ -2130,7 +2118,6 @@ primOpHasSideEffects WriteMutVarOp	   = True
 primOpHasSideEffects UnsafeFreezeArrayOp	= True
 primOpHasSideEffects UnsafeFreezeByteArrayOp	= True
 primOpHasSideEffects UnsafeThawArrayOp		= True
-primOpHasSideEffects UnsafeThawByteArrayOp	= True
 
 primOpHasSideEffects TakeMVarOp        = True
 primOpHasSideEffects PutMVarOp         = True
diff --git a/ghc/includes/PrimOps.h b/ghc/includes/PrimOps.h
index 4a0f952cd54878fa06acd4ad887e27327b5b7a14..1ce766d0df0640fe979b3c6d6e689d5355af7a64 100644
--- a/ghc/includes/PrimOps.h
+++ b/ghc/includes/PrimOps.h
@@ -1,5 +1,5 @@
 /* -----------------------------------------------------------------------------
- * $Id: PrimOps.h,v 1.45 2000/01/18 12:37:33 simonmar Exp $
+ * $Id: PrimOps.h,v 1.46 2000/03/13 12:11:43 simonmar Exp $
  *
  * (c) The GHC Team, 1998-1999
  *
@@ -595,7 +595,6 @@ extern I_ resetGenSymZh(void);
 	}
 
 #define unsafeFreezzeByteArrayzh(r,a)	r=(a)
-#define unsafeThawByteArrayzh(r,a)	r=(a)
 
 EF_(unsafeThawArrayzh_fast);
 
diff --git a/ghc/lib/std/PrelGHC.hi-boot b/ghc/lib/std/PrelGHC.hi-boot
index 6d86963e59d6fb5a5e4a1730def6712a7b8abf50..94075d65e6332f9f4d437ab575234e8724c3432a 100644
--- a/ghc/lib/std/PrelGHC.hi-boot
+++ b/ghc/lib/std/PrelGHC.hi-boot
@@ -295,7 +295,6 @@ __export PrelGHC
   unsafeFreezzeByteArrayzh	-- Ditto
 
   unsafeThawArrayzh
-  unsafeThawByteArrayzh
 
   sizzeofByteArrayzh		-- Ditto
   sizzeofMutableByteArrayzh	-- Ditto