diff --git a/include/clang/AST/Stmt.h b/include/clang/AST/Stmt.h
index 7ede9ce..d1f7d66 100644
--- a/include/clang/AST/Stmt.h
+++ b/include/clang/AST/Stmt.h
@@ -1328,7 +1328,8 @@
   }
 
   Expr *getInputExpr(unsigned i);
-
+  void setInputExpr(unsigned i, Expr *E);
+  
   const Expr *getInputExpr(unsigned i) const {
     return const_cast<AsmStmt*>(this)->getInputExpr(i);
   }
diff --git a/lib/AST/Stmt.cpp b/lib/AST/Stmt.cpp
index 7e73f02..8a80275 100644
--- a/lib/AST/Stmt.cpp
+++ b/lib/AST/Stmt.cpp
@@ -218,6 +218,10 @@
 Expr *AsmStmt::getInputExpr(unsigned i) {
   return cast<Expr>(Exprs[i + NumOutputs]);
 }
+void AsmStmt::setInputExpr(unsigned i, Expr *E) {
+  Exprs[i + NumOutputs] = E;
+}
+
 
 /// getInputConstraint - Return the specified input constraint.  Unlike output
 /// constraints, these can be empty.
diff --git a/lib/Sema/SemaStmt.cpp b/lib/Sema/SemaStmt.cpp
index 6801dd4..3815dea 100644
--- a/lib/Sema/SemaStmt.cpp
+++ b/lib/Sema/SemaStmt.cpp
@@ -1542,8 +1542,9 @@
     if (!Info.hasTiedOperand()) continue;
 
     unsigned TiedTo = Info.getTiedOperand();
+    unsigned InputOpNo = i+NumOutputs;
     Expr *OutputExpr = Exprs[TiedTo];
-    Expr *InputExpr = Exprs[i+NumOutputs];
+    Expr *InputExpr = Exprs[InputOpNo];
     QualType InTy = InputExpr->getType();
     QualType OutTy = OutputExpr->getType();
     if (Context.hasSameType(InTy, OutTy))
@@ -1588,7 +1589,7 @@
     
     // If this is a reference to the input and if the input was the smaller
     // one, then we have to reject this asm.
-    if (isOperandMentioned(i+NumOutputs, Pieces)) {
+    if (isOperandMentioned(InputOpNo, Pieces)) {
       // This is a use in the asm string of the smaller operand.  Since we
       // codegen this by promoting to a wider value, the asm will get printed
       // "wrong".
@@ -1607,6 +1608,19 @@
         OutputConstraintInfos[TiedTo].allowsRegister())
       continue;
     
+    // Either both of the operands were mentioned or the smaller one was
+    // mentioned.  One more special case that we'll allow: if the tied input is
+    // integer, unmentioned, and is a constant, then we'll allow truncating it
+    // down to the size of the destination.
+    if (InputDomain == AD_Int && OutputDomain == AD_Int &&
+        !isOperandMentioned(InputOpNo, Pieces) &&
+        InputExpr->isEvaluatable(Context)) {
+      ImpCastExprToType(InputExpr, OutTy, CK_IntegralCast);
+      Exprs[InputOpNo] = InputExpr;
+      NS->setInputExpr(i, InputExpr);
+      continue;
+    }
+    
     Diag(InputExpr->getLocStart(),
          diag::err_asm_tying_incompatible_types)
       << InTy << OutTy << OutputExpr->getSourceRange()
diff --git a/test/CodeGen/asm-inout.c b/test/CodeGen/asm-inout.c
index 5b0a5f7..29142f7 100644
--- a/test/CodeGen/asm-inout.c
+++ b/test/CodeGen/asm-inout.c
@@ -29,3 +29,12 @@
 		: "edi"
 		);
 }
+
+// PR8959 - This should implicitly truncate the immediate to a byte.
+int test4(volatile int *addr) {
+  unsigned char oldval;
+  __asm__ ("frob %0" : "=r"(oldval) : "0"(0xff));
+  return (int)oldval;
+// CHECK: call i8 asm "frob $0", "=r,0{{.*}}"(i8 -1)
+}
+