diff --git a/lib/CodeGen/SimpleRegisterCoalescing.cpp b/lib/CodeGen/SimpleRegisterCoalescing.cpp
index ba026d7..c723c9e 100644
--- a/lib/CodeGen/SimpleRegisterCoalescing.cpp
+++ b/lib/CodeGen/SimpleRegisterCoalescing.cpp
@@ -457,8 +457,14 @@
       O.setSubReg(0);
     } else {
       unsigned OldSubIdx = O.getSubReg();
-      assert((!SubIdx || !OldSubIdx) && "Conflicting sub-register index!");
-      if (SubIdx)
+      // Sub-register indexes goes from small to large. e.g.
+      // RAX: 0 -> AL, 1 -> AH, 2 -> AX, 3 -> EAX
+      // EAX: 0 -> AL, 1 -> AH, 2 -> AX
+      // So RAX's sub-register 2 is AX, RAX's sub-regsiter 3 is EAX, whose
+      // sub-register 2 is also AX.
+      if (SubIdx && OldSubIdx && SubIdx != OldSubIdx)
+        assert(OldSubIdx < SubIdx && "Conflicting sub-register index!");
+      else if (SubIdx)
         O.setSubReg(SubIdx);
       O.setReg(DstReg);
     }
diff --git a/test/CodeGen/X86/2008-02-25-X86-64-CoalescerBug.ll b/test/CodeGen/X86/2008-02-25-X86-64-CoalescerBug.ll
new file mode 100644
index 0000000..5d60bde
--- /dev/null
+++ b/test/CodeGen/X86/2008-02-25-X86-64-CoalescerBug.ll
@@ -0,0 +1,55 @@
+; RUN: llvm-as < %s | llc -march=x86-64
+
+	%struct.XX = type <{ i8 }>
+	%struct.YY = type { i64 }
+	%struct.ZZ = type opaque
+
+define i8 @f(%struct.XX*** %fontMap, %struct.XX* %uen) signext  {
+entry:
+	%tmp45 = add i16 0, 1		; <i16> [#uses=2]
+	br i1 false, label %bb124, label %bb53
+
+bb53:		; preds = %entry
+	%tmp55 = call %struct.YY** @AA( i64 1, %struct.XX* %uen )		; <%struct.YY**> [#uses=3]
+	%tmp2728128 = load %struct.XX** null		; <%struct.XX*> [#uses=1]
+	%tmp61 = load %struct.YY** %tmp55, align 8		; <%struct.YY*> [#uses=1]
+	%tmp62 = getelementptr %struct.YY* %tmp61, i32 0, i32 0		; <i64*> [#uses=1]
+	%tmp63 = load i64* %tmp62, align 8		; <i64> [#uses=1]
+	%tmp6566 = zext i16 %tmp45 to i64		; <i64> [#uses=1]
+	%tmp67 = shl i64 %tmp6566, 1		; <i64> [#uses=1]
+	call void @BB( %struct.YY** %tmp55, i64 %tmp67, i8 signext  0, %struct.XX* %uen )
+	%tmp121131 = icmp eq i16 %tmp45, 1		; <i1> [#uses=1]
+	br i1 %tmp121131, label %bb124, label %bb70.preheader
+
+bb70.preheader:		; preds = %bb53
+	%tmp72 = bitcast %struct.XX* %tmp2728128 to %struct.ZZ***		; <%struct.ZZ***> [#uses=1]
+	br label %bb70
+
+bb70:		; preds = %bb119, %bb70.preheader
+	%indvar133 = phi i32 [ %indvar.next134, %bb119 ], [ 0, %bb70.preheader ]		; <i32> [#uses=2]
+	%tmp.135 = trunc i64 %tmp63 to i32		; <i32> [#uses=1]
+	%tmp136 = shl i32 %indvar133, 1		; <i32> [#uses=1]
+	%DD = add i32 %tmp136, %tmp.135		; <i32> [#uses=1]
+	%tmp73 = load %struct.ZZ*** %tmp72, align 8		; <%struct.ZZ**> [#uses=0]
+	br i1 false, label %bb119, label %bb77
+
+bb77:		; preds = %bb70
+	%tmp8384 = trunc i32 %DD to i16		; <i16> [#uses=1]
+	%tmp85 = sub i16 0, %tmp8384		; <i16> [#uses=1]
+	store i16 %tmp85, i16* null, align 8
+	call void @CC( %struct.YY** %tmp55, i64 0, i64 2, i8* null, %struct.XX* %uen )
+	ret i8 0
+
+bb119:		; preds = %bb70
+	%indvar.next134 = add i32 %indvar133, 1		; <i32> [#uses=1]
+	br label %bb70
+
+bb124:		; preds = %bb53, %entry
+	ret i8 undef
+}
+
+declare %struct.YY** @AA(i64, %struct.XX*)
+
+declare void @BB(%struct.YY**, i64, i8 signext , %struct.XX*)
+
+declare void @CC(%struct.YY**, i64, i64, i8*, %struct.XX*)