diff --git a/gas/ChangeLog b/gas/ChangeLog
index f19ed52500..b6440a7fc9 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,8 @@
+2007-04-19  Paul Brook  <paul@codesourcery.com>
+
+	* config/tc-arm.c (md_assemble): Only allow 16-bit instructions on
+	Thumb-1.  Add sanity check for bogus relaxations.
+
 2007-04-19  Paul Brook  <paul@codesourcery.com>
 
 	* config/tc-arm.c (insns): Allow rsb and rsbs on Thumb-1.
diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 4e3afec059..62360f11e2 100644
--- a/gas/config/tc-arm.c
+++ b/gas/config/tc-arm.c
@@ -14110,6 +14110,14 @@ md_assemble (char *str)
 	  return;
 	}
 
+      if (!ARM_CPU_HAS_FEATURE (variant, arm_ext_v6t2) && !inst.size_req)
+	{
+	  /* Implicit require narrow instructions on Thumb-1.  This avoids
+	     relaxation accidentally introducing Thumb-2 instructions.  */
+	  if (opcode->tencode != do_t_blx && opcode->tencode != do_t_branch23)
+	    inst.size_req = 2;
+	}
+
       /* Check conditional suffixes.  */
       if (current_it_mask)
 	{
@@ -14151,6 +14159,11 @@ md_assemble (char *str)
 	      return;
 	    }
 	}
+
+      /* Something has gone badly wrong if we try to relax a fixed size
+         instruction.  */
+      assert (inst.size_req == 0 || !inst.relax);
+
       ARM_MERGE_FEATURE_SETS (thumb_arch_used, thumb_arch_used,
 			      *opcode->tvariant);
       /* Many Thumb-2 instructions also have Thumb-1 variants, so explicitly
diff --git a/gas/testsuite/ChangeLog b/gas/testsuite/ChangeLog
index d3dfee25fd..10af40ceaf 100644
--- a/gas/testsuite/ChangeLog
+++ b/gas/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2007-04-19  Paul Brook  <paul@codesourcery.com>
+
+	* gas/arm/thumb1_unified.d: New test.
+	* gas/arm/thumb1_unified.s: New test.
+
 2007-04-19  Nathan Froyd <froydnj@codesourcery.com>
 
 	* gas/ppc/booke.s: Add tlbsx, tlbsxe.
diff --git a/gas/testsuite/gas/arm/thumb1_unified.d b/gas/testsuite/gas/arm/thumb1_unified.d
new file mode 100644
index 0000000000..c2fdf30632
--- /dev/null
+++ b/gas/testsuite/gas/arm/thumb1_unified.d
@@ -0,0 +1,20 @@
+# name: Thumb-1 unified
+# objdump: -dr --prefix-addresses --show-raw-insn
+
+.*: +file format .*arm.*
+
+Disassembly of section .text:
+0[0-9a-f]+ <[^>]+> 200c      	movs	r0, #12
+0[0-9a-f]+ <[^>]+> 1cd1      	adds	r1, r2, #3
+0[0-9a-f]+ <[^>]+> 1ed1      	subs	r1, r2, #3
+0[0-9a-f]+ <[^>]+> 3364      	adds	r3, #100
+0[0-9a-f]+ <[^>]+> 3c83      	subs	r4, #131
+0[0-9a-f]+ <[^>]+> 2d27      	cmp	r5, #39
+0[0-9a-f]+ <[^>]+> a103      	add	r1, pc, #12	\(adr [^)]*\)
+0[0-9a-f]+ <[^>]+> 4a03      	ldr	r2, \[pc, #12\]	\([^)]*\)
+0[0-9a-f]+ <[^>]+> 6863      	ldr	r3, \[r4, #4\]
+0[0-9a-f]+ <[^>]+> 9d01      	ldr	r5, \[sp, #4\]
+0[0-9a-f]+ <[^>]+> b001      	add	sp, #4
+0[0-9a-f]+ <[^>]+> b081      	sub	sp, #4
+0[0-9a-f]+ <[^>]+> af01      	add	r7, sp, #4
+0[0-9a-f]+ <[^>]+> 4251      	negs	r1, r2
diff --git a/gas/testsuite/gas/arm/thumb1_unified.s b/gas/testsuite/gas/arm/thumb1_unified.s
new file mode 100644
index 0000000000..c8da6ec5aa
--- /dev/null
+++ b/gas/testsuite/gas/arm/thumb1_unified.s
@@ -0,0 +1,25 @@
+.text
+.arch armv4t
+.syntax unified
+.thumb
+foo:
+movs r0, #12
+adds r1, r2, #3
+subs r1, r2, #3
+adds r3, r3, #0x64
+subs r4, r4, #0x83
+cmp r5, #0x27
+
+adr r1, bar
+ldr r2, bar
+ldr r3, [r4, #4]
+ldr r5, [sp, #4]
+add sp, sp, #4
+sub sp, sp, #4
+add r7, sp, #4
+
+rsbs r1, r2, #0
+
+.align 2
+bar:
+