diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -11657,7 +11657,8 @@
    should perform tail call optimization. The ``tail`` marker is a hint that
    `can be ignored <CodeGenerator.html#sibcallopt>`_. The ``musttail`` marker
    means that the call must be tail call optimized in order for the program to
-   be correct. The ``musttail`` marker provides these guarantees:
+   be correct. This is true even in the presence of attributes like
+   "disable-tail-calls". The ``musttail`` marker provides these guarantees:
 
    #. The call will not cause unbounded stack growth if it is part of a
       recursive cycle in the call graph.
diff --git a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -1139,9 +1139,8 @@
   bool IsTailCall = CI->isTailCall();
   if (IsTailCall && !isInTailCallPosition(*CI, TM))
     IsTailCall = false;
-  if (IsTailCall && MF->getFunction()
-                            .getFnAttribute("disable-tail-calls")
-                            .getValueAsBool())
+  if (IsTailCall && !CI->isMustTailCall() &&
+      MF->getFunction().getFnAttribute("disable-tail-calls").getValueAsBool())
     IsTailCall = false;
 
   CallLoweringInfo CLI;
diff --git a/llvm/test/CodeGen/X86/fast-isel-disable-tail-calls.ll b/llvm/test/CodeGen/X86/fast-isel-disable-tail-calls.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/X86/fast-isel-disable-tail-calls.ll
@@ -0,0 +1,9 @@
+; RUN: llc -O0 -fast-isel -mtriple=x86_64-unknown-unknown < %s | FileCheck %s
+
+; CHECK-NOT: retq
+; CHECK: jmpq
+
+define void @f(ptr %this) "disable-tail-calls"="true" {
+  musttail call void %this(ptr %this)
+  ret void
+}