diff --git a/mach/powerpc/libem/aar4.s b/mach/powerpc/libem/aar4.s
index fc8620d02..08390b081 100644
--- a/mach/powerpc/libem/aar4.s
+++ b/mach/powerpc/libem/aar4.s
@@ -8,21 +8,17 @@
 
 .define .aar4
 .aar4:
-	lis r0, hi16[.trap_earray]
-	ori r0, r0, lo16[.trap_earray]
-	mtspr ctr, r0            ! load CTR with trap address
-
 	lwz r4, 0(sp)            ! r4 = address of descriptor
 	lwz r5, 4(sp)            ! r5 = index
 	lwz r6, 8(sp)            ! r6 = address of array
 
 	lwz r0, 0(r4)
 	subf. r5, r0, r5         ! subtract lower bound from index
-	bltctr                   ! check lower bound
+	blt .trap_earray         ! check lower bound
 
 	lwz r0, 4(r4)
 	cmplw r5, r0
-	bgtctr                   ! check upper bound
+	bgt .trap_earray         ! check upper bound
 
 	lwz r3, 8(r4)            ! r3 = size of element
 	mullw r5, r5, r3         ! scale index by size
@@ -30,3 +26,7 @@
 	stw r6, 8(sp)            ! push address of element
 	addi sp, sp, 8
 	blr
+
+.trap_earray:
+	li r3, 0                 ! EARRAY = 0 in h/em_abs.h
+	b .trp
diff --git a/mach/powerpc/libem/build.lua b/mach/powerpc/libem/build.lua
index cb5efd281..ac84e3b0f 100644
--- a/mach/powerpc/libem/build.lua
+++ b/mach/powerpc/libem/build.lua
@@ -6,7 +6,7 @@ for _, plat in ipairs(vars.plats) do
 	acklibrary {
 		name = "lib_"..plat,
 		srcs = {
-			"./*.s", -- exg.s
+			"./*.s", -- trp.s
 		},
 		vars = { plat = plat },
 		deps = {
@@ -15,4 +15,3 @@ for _, plat in ipairs(vars.plats) do
 		}
 	}
 end
-
diff --git a/mach/powerpc/libem/csa.s b/mach/powerpc/libem/csa.s
index 3898241c4..86d792554 100644
--- a/mach/powerpc/libem/csa.s
+++ b/mach/powerpc/libem/csa.s
@@ -13,22 +13,21 @@
 	lwz r4, 4(sp)
 	addi sp, sp, 8
 
-	lwz r5, 0(r3)            ! load default
-	mtspr ctr, r5
-	
-	lwz r5, 4(r3)            ! fetch lower bound
-	subf. r4, r5, r4         ! adjust value
-	bltctr                   ! jump to default if out of range
+	lwz r5, 0(r3)            ! r5 = default target
 
-	lwz r5, 8(r3)            ! fetch range
-	cmplw r4, r5
-	bgtctr                   ! jump to default if out of range
+	lwz r6, 4(r3)            ! fetch lower bound
+	subf. r4, r6, r4         ! adjust value
+	blt 1f                   ! jump to default if out of range
+
+	lwz r6, 8(r3)            ! fetch range
+	cmplw r4, r6
+	bgt 1f                   ! jump to default if out of range
 
 	addi r3, r3, 12          ! skip header
 	slwi r4, r4, 2           ! scale value (<<2)
-	lwzx r5, r3, r4          ! load target
-	mtspr ctr, r5
+	lwzx r5, r3, r4          ! r5 = new target
 
-	or. r5, r5, r5           ! test it
+1:	mtspr ctr, r5
+	mr. r5, r5               ! test it
 	bnectr                   ! jump to target if non-zero
 	b .trap_ecase            ! otherwise trap
diff --git a/mach/powerpc/libem/csb.s b/mach/powerpc/libem/csb.s
index 571bfc210..92c6d096d 100644
--- a/mach/powerpc/libem/csb.s
+++ b/mach/powerpc/libem/csb.s
@@ -13,23 +13,20 @@
 	lwz r4, 4(sp)
 	addi sp, sp, 8
 
-	lwz r5, 0(r3)            ! load default
-	mtspr ctr, r5
+	lwz r5, 0(r3)            ! r5 = default target
 
 	lwz r6, 4(r3)            ! fetch count
-
-1:
-	or. r6, r6, r6           ! test count
-	beqctr                   ! exit if zero
-	addi r6, r6, -1          ! otherwise decrement
-
-	lwzu r7, 8(r3)           ! fetch target index, increment pointer
+	mr. r6, r6               ! skip loop if count is zero
+	beq 3f                   !   (needed by Modula-2 "CASE i OF END")
+	mtspr ctr, r6
+1:	lwzu r7, 8(r3)           ! fetch target index, increment pointer
 	cmpw r4, r7              ! compare with value
-	bne 1b                   ! if not equal, go again
+	beq 2f
+	bdnz 1b                  ! if not equal, go again
+	b 3f
 
-	lwz r7, 4(r3)            ! fetch target address
-	mtspr ctr, r7
-
-	or. r7, r7, r7           ! test it
+2:	lwz r5, 4(r3)            ! r5 = new target
+3:	mtspr ctr, r5
+	mr. r5, r5               ! test target
 	bnectr                   ! jump to target if non-zero
 	b .trap_ecase            ! otherwise trap
diff --git a/mach/powerpc/libem/rck.s b/mach/powerpc/libem/rck.s
index 9008be610..f1cf7f848 100644
--- a/mach/powerpc/libem/rck.s
+++ b/mach/powerpc/libem/rck.s
@@ -18,3 +18,7 @@
     bgt .trap_erange
 
     blr
+
+.trap_erange:
+    li r3, 1       ! ERANGE = 1 in h/em_abs.h
+    b .trp
diff --git a/mach/powerpc/libem/trp.s b/mach/powerpc/libem/trp.s
new file mode 100644
index 000000000..b07afb929
--- /dev/null
+++ b/mach/powerpc/libem/trp.s
@@ -0,0 +1,56 @@
+.sect .text
+
+.define .trap_ecase
+.trap_ecase:
+	li	r3, 20			! ECASE = 20 in h/em_abs.h
+	! FALLTHROUGH to .trp
+
+! Raises an EM trap.
+! Expects r3 = trap number.
+
+.define .trp
+.trp:
+	cmplwi	r3, 15			! traps > 15 can't be ignored
+	bgt	1f
+
+	lis	r4, ha16[.ignmask]
+	lwz	r4, lo16[.ignmask](r4)	! load ignore mask
+	srw	r4, r4, r3
+	andi.	r4, r4, 1
+	bnelr				! return if ignoring trap
+
+1:	lis	r4, ha16[.trppc]
+	lwz	r5, lo16[.trppc](r4)	! r5 = user trap routine
+	mr.	r5, r5
+	beq	2f			! if no user trap routine, bail out
+
+	mtspr	ctr, r5
+	mfspr	r6, lr
+	li	r0, 0
+	stwu	r3, -8(sp)		! push trap number
+	stw	r0, lo16[.trppc](r4)	! reset trap routine
+	stw	r6, 4(sp)		! save old lr
+	bctrl				! call trap routine
+
+	lwz	r0, 4(sp)
+	mtspr	lr, r0
+	addi	sp, sp, 8		! retract over stack usage
+	blr
+
+2:	! No trap handler.  Write error message, exit.
+	li	r3, 2
+	stwu	r3, -12(sp)
+	lis	r4, ha16[message]
+	addi	r4, r4, lo16[message]
+	li	r5, 6
+	stw	r4, 4(sp)
+	stw	r5, 8(sp)
+	bl	_write			! write(2, message, 6)
+
+	li	r3, 1
+	stw	r3, 0(sp)
+	bl	__exit			! _exit(1)
+
+.sect .rom
+message:
+	.ascii "TRAP!\n"
diff --git a/mach/powerpc/ncg/table b/mach/powerpc/ncg/table
index e66ae855f..10ffadb16 100644
--- a/mach/powerpc/ncg/table
+++ b/mach/powerpc/ncg/table
@@ -2168,10 +2168,13 @@ PATTERNS
 	pat trp                            /* Raise EM trap */
 		with REG3
 			kills ALL
-			gen bl {LABEL, ".trap"}
+			gen bl {LABEL, ".trp"}
 
-	pat sig                            /* Set trap handler */
-		leaving ste ".trppc"
+	pat sig                            /* Set trap handler, yield old */
+		leaving
+			loe ".trppc"
+			exg 4
+			ste ".trppc"
 
 	pat rtt                            /* Return from trap */
 		leaving ret 0
@@ -2216,22 +2219,14 @@ PATTERNS
 		with REG
 			gen move %1, sp
 
-	pat lae rck $2==4                  /* Range check */
-		with REG
-			kills ALL
-			gen
-				cmpwi %1, {C, rom($1, 1)}
-				blt {LABEL, ".trap_erange"}
-				cmpwi %1, {C, rom($1, 2)}
-				bgt {LABEL, ".trap_erange"}
-			yields %1
+	pat rck $1==4                      /* Range check */
+		leaving cal ".rck"
 
 
 /* Single-precision floating-point */
 
 	pat zrf $1==4                      /* Push zero */
-		leaving
-			loe ".fs_00000000"
+		leaving loe ".fs_00000000"
 
 	pat adf $1==4                      /* Add single */
 		with FSREG FSREG
diff --git a/plat/linuxppc/libsys/build.lua b/plat/linuxppc/libsys/build.lua
index f7b16b378..696c62d42 100644
--- a/plat/linuxppc/libsys/build.lua
+++ b/plat/linuxppc/libsys/build.lua
@@ -4,7 +4,6 @@ acklibrary {
 		"./_syscall.s",
 		"./sigaction.s",
 		"./signal.c",
-		"./trap.s",
 		"plat/linux/libsys/_exit.c",
 		"plat/linux/libsys/_hol0.s",
 		"plat/linux/libsys/close.c",
diff --git a/plat/linuxppc/libsys/trap.s b/plat/linuxppc/libsys/trap.s
deleted file mode 100644
index 93c5189a4..000000000
--- a/plat/linuxppc/libsys/trap.s
+++ /dev/null
@@ -1,112 +0,0 @@
-#
-! $Source: /cvsroot/tack/Ack/plat/linux386/libsys/_syscall.s,v $
-! $State: Exp $
-! $Revision: 1.1 $
-
-! Declare segments (the order is important).
-
-.sect .text
-.sect .rom
-.sect .data
-.sect .bss
-
-.sect .text
-
-#define IFFALSE 4
-#define IFTRUE 12
-#define ALWAYS 20
-
-#define LT 0
-#define GT 1
-#define EQ 2
-#define OV 3
-
-EARRAY	=  0
-ERANGE	=  1
-ESET	=  2
-EIOVFL	=  3
-EFOVFL	=  4
-EFUNFL	=  5
-EIDIVZ	=  6
-EFDIVZ	=  7
-EIUND	=  8
-EFUND	=  9
-ECONV	= 10
-ESTACK  = 16
-EHEAP	= 17
-EILLINS = 18
-EODDZ	= 19
-ECASE	= 20
-EMEMFLT	= 21
-EBADPTR = 22
-EBADPC  = 23
-EBADLAE = 24
-EBADMON = 25
-EBADLIN = 26
-EBADGTO = 27
-EUNIMPL = 63		! unimplemented em-instruction called
-
-! EM trap handling.
-
-.define .trap_ecase
-.trap_ecase:
-	addi r3, r0, ECASE
-	b .trap
-
-.define .trap_earray
-.trap_earray:
-	addi r3, r0, EARRAY
-	b .trap
-
-.define .trap_erange
-.trap_erange:
-	addi r3, r0, ERANGE
-	b .trap
-
-.define .trp
-.define .trap
-.trp:
-.trap:
-	cmpi cr0, 0, r3, 15      ! traps >15 can't be ignored
-	bc IFTRUE, LT, 1f
-
-	addi r4, r0, 1
-	rlwnm r4, r4, r3, 0, 31  ! calculate trap bit
-	li32 r5, .ignmask
-	lwz r5, 0(r5)            ! load ignore mask
-	and. r4, r4, r5          ! compare
-	bclr IFFALSE, EQ, 0      ! return if non-zero
-
-1:
-	li32 r4, .trppc
-	lwz r5, 0(r4)            ! load user trap routine
-	or. r5, r5, r5           ! test
-	bc IFTRUE, EQ, fatal     ! if no user trap routine, bail out
-
-	addi r0, r0, 0
-	stw r0, 0(r4)            ! reset trap routine
-
-	mfspr r0, lr
-	stwu r0, -4(sp)          ! save old lr
-
-	stwu r3, -4(sp)
-	mtspr ctr, r5
-	bcctrl ALWAYS, 0, 0      ! call trap routine
-
-	lwz r0, 4(sp)            ! load old lr again
-	addi sp, sp, 8           ! retract over stack usage
-	bclr ALWAYS, 0, 0        ! return
-
-fatal:
-	addi r3, r0, 1
-	li32 r4, message
-	addi r5, r0, 6
-	addi r0, r0, 4           ! write()
-	sc 0
-
-	addi r0, r0, 1           ! exit()
-	sc 0
-
-.sect .rom
-message:
-	.ascii "TRAP!\n"
diff --git a/plat/osxppc/libsys/build.lua b/plat/osxppc/libsys/build.lua
index 072730b7a..49fc0c934 100644
--- a/plat/osxppc/libsys/build.lua
+++ b/plat/osxppc/libsys/build.lua
@@ -19,7 +19,6 @@ acklibrary {
 		"./sigaction.s",
 		"./stat.s",
 		"./write.s",
-		"plat/linuxppc/libsys/trap.s",
 		"plat/osx/libsys/brk.c",
 		"plat/osx/libsys/creat.c",
 		"plat/osx/libsys/isatty.c",
diff --git a/tests/plat/build.lua b/tests/plat/build.lua
index 666af7d95..fdac9bae3 100644
--- a/tests/plat/build.lua
+++ b/tests/plat/build.lua
@@ -13,6 +13,7 @@ definerule("plat_testsuite",
 			"tests/plat/dup_e.e",
 			"tests/plat/exg_e.e",
 			"tests/plat/inn_e.e",
+			"tests/plat/rck_e.e",
 			"tests/plat/rotate_e.e",
 			"tests/plat/*.p",
 			"tests/plat/b/*.b",
diff --git a/tests/plat/rck_e.e b/tests/plat/rck_e.e
new file mode 100644
index 000000000..cd5c581df
--- /dev/null
+++ b/tests/plat/rck_e.e
@@ -0,0 +1,186 @@
+#
+    mes 2, EM_WSIZE, EM_PSIZE
+
+/*
+ * Uses _rck_ for range checks.  Catches the EM trap if a value is out
+ * of range, and continues with the next instruction after _rck_.
+ *
+ * Some back ends, like i80, ignore _rck_, so this test fails.
+ */
+
+testnr
+    con 1         ; test number
+caught
+    con 0         ; number of caught traps
+
+    inp $next
+    inp $catch
+    inp $never
+    exp $_m_a_i_n
+    pro $_m_a_i_n,0
+
+    lim           ; load ignore mask
+    loc 2
+    and EM_WSIZE  ; check bit 1 << ERANGE
+    zeq *1        ; fail if ignoring ERANGE
+.1
+    rom 1I4
+    lae .1
+    loi 4
+    cal $fail
+    asp 4
+1
+
+    cal $next     ; increment testnr, catch next trap
+    loc 10125
+.2
+    rom 4283, 13644
+    lae .2
+    rck EM_WSIZE  ; testnr 2 in range
+    asp EM_WSIZE
+
+    cal $next
+    loc 4282
+    lae .2
+    rck EM_WSIZE  ; testnr 3 out of range
+    asp EM_WSIZE
+
+    cal $next
+    loc 4283
+    lae .2
+    rck EM_WSIZE  ; testnr 4 in range
+    asp EM_WSIZE
+
+    cal $next
+    loc 13644
+    lae .2
+    rck EM_WSIZE  ; testnr 5 in range
+    asp EM_WSIZE
+
+    cal $next
+    loc 13655
+    lae .2
+    rck EM_WSIZE  ; testnr 6 out of range
+    asp EM_WSIZE
+
+    cal $next
+    loc -13015
+.7
+    rom -31344, -1898
+    lae .7
+    rck EM_WSIZE  ; testnr 7 in range
+    asp EM_WSIZE
+
+    cal $next
+    loc 8580
+.8
+    rom -26315, 4588
+    lae .8
+    rck EM_WSIZE  ; testnr 8 out of range
+    asp EM_WSIZE
+
+    ; The last test raised a trap, so now there is no trap handler.
+    lpi $never
+    sig           ; push old trap handler
+    loc 0
+    loc EM_WSIZE
+    loc EM_PSIZE
+    cuu           ; push NULL pointer
+    cmp
+    zeq *17       ; fail unless old handler is NULL
+.17
+    rom 17I4
+    lae .17
+    loi 4
+    cal $fail
+    asp 4
+17
+    ; Change the trap handler from $never to $catch.
+    lpi $catch
+    sig
+    lpi $never
+    cmp
+    zeq *18
+.18
+    rom 18I4
+    lae .18
+    loi 4
+    cal $fail
+    asp 4
+18
+    ; Begin ignoring range traps.
+    loc 2         ; 1 << ERANGE
+    sim
+    loc 18
+    ste testnr
+    loc 8580
+    lae .8
+    rck EM_WSIZE  ; testnr 18 out of range but ignored
+
+    ; Fail if we caught the wrong number of traps.
+    loe caught
+    loc 3
+    beq *20
+.20
+    rom 20I4
+    lae .20
+    loi 4
+    cal $fail
+    asp 4
+20
+    cal $finished
+    end
+
+    pro $next,0
+    ine testnr    ; next test
+    lpi $catch
+    sig           ; catch next EM trap (only one trap)
+    asp EM_PSIZE
+    ret 0
+    end
+
+    pro $catch,0
+    ine caught    ; count this trap
+
+    lol 0         ; load trap number
+    loc 1
+    beq *1        ; fail if trap != ERANGE
+.101
+    rom 257I4
+    lae .101
+    loi 4
+    cal $fail
+    ; Wrong type of trap.  _rtt_ might not work, so exit now.
+    cal $finished
+1
+    ; Fail if the wrong test raised this trap.
+    loe testnr
+    loc 3
+    beq *2
+    loe testnr
+    loc 6
+    beq *2
+    loe testnr
+    loc 8
+    beq *2
+    loc 256
+    loe testnr
+    adi EM_WSIZE  ; 0x100 + testnr
+    loc EM_WSIZE
+    loc 4
+    cuu
+    cal $fail
+    asp 4
+2
+    rtt           ; return from trap handler
+    end
+
+    pro $never,0
+.200
+    rom 200I4
+    lae .200
+    loi 4
+    cal $fail
+    asp 4
+    rtt
+    end