diff --git a/lib/Target/X86/X86RegisterInfo.cpp b/lib/Target/X86/X86RegisterInfo.cpp
index 2b14f6e..0d528f7 100644
--- a/lib/Target/X86/X86RegisterInfo.cpp
+++ b/lib/Target/X86/X86RegisterInfo.cpp
@@ -1121,11 +1121,18 @@
 
     virtual bool runOnMachineFunction(MachineFunction &MF) {
       MachineFrameInfo *FFI = MF.getFrameInfo();
+      MachineRegisterInfo &RI = MF.getRegInfo();
 
-      // Calculate and set max stack object alignment early, so we can decide
-      // whether we will need stack realignment (and thus FP).
+      // Calculate max stack alignment of all already allocated stack objects.
       unsigned MaxAlign = calculateMaxStackAlignment(FFI);
 
+      // Be over-conservative: scan over all vreg defs and find, whether vector
+      // registers are used. If yes - there is probability, that vector register
+      // will be spilled and thus stack needs to be aligned properly.
+      for (unsigned RegNum = TargetRegisterInfo::FirstVirtualRegister;
+           RegNum < RI.getLastVirtReg(); ++RegNum)
+        MaxAlign = std::max(MaxAlign, RI.getRegClass(RegNum)->getAlignment());
+
       FFI->setMaxAlignment(MaxAlign);
 
       return false;
diff --git a/lib/Target/X86/X86TargetMachine.cpp b/lib/Target/X86/X86TargetMachine.cpp
index f75a77c..218f356 100644
--- a/lib/Target/X86/X86TargetMachine.cpp
+++ b/lib/Target/X86/X86TargetMachine.cpp
@@ -162,6 +162,8 @@
 }
 
 bool X86TargetMachine::addPreRegAlloc(PassManagerBase &PM, bool Fast) {
+  // Calculate and set max stack object alignment early, so we can decide
+  // whether we will need stack realignment (and thus FP).
   PM.add(createX86MaxStackAlignmentCalculatorPass());
   return false;  // -print-machineinstr shouldn't print after this.
 }