diff --git a/docs/GlobalISel/GenericOpcode.rst b/docs/GlobalISel/GenericOpcode.rst
index 3110e1fa839..7c418a0c05c 100644
--- a/docs/GlobalISel/GenericOpcode.rst
+++ b/docs/GlobalISel/GenericOpcode.rst
@@ -672,12 +672,9 @@ Other Operations
 G_DYN_STACKALLOC
 ^^^^^^^^^^^^^^^^
 
-Dynamically realign the stack pointer to the specified alignment
+Dynamically realigns the stack pointer to the specified size and alignment.
+An alignment value of `0` or `1` mean no specific alignment.
 
 .. code-block:: none
 
   %8:_(p0) = G_DYN_STACKALLOC %7(s64), 32
-
-.. caution::
-
-  What does it mean for the immediate to be 0? It happens in the tests
diff --git a/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index bb144480bbd..3c24933921b 100644
--- a/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -4891,7 +4891,7 @@ LegalizerHelper::LegalizeResult
 LegalizerHelper::lowerDynStackAlloc(MachineInstr &MI) {
   Register Dst = MI.getOperand(0).getReg();
   Register AllocSize = MI.getOperand(1).getReg();
-  unsigned Align = MI.getOperand(2).getImm();
+  Align Alignment = assumeAligned(MI.getOperand(2).getImm());
 
   const auto &MF = *MI.getMF();
   const auto &TLI = *MF.getSubtarget().getTargetLowering();
@@ -4907,8 +4907,8 @@ LegalizerHelper::lowerDynStackAlloc(MachineInstr &MI) {
   // have to generate an extra instruction to negate the alloc and then use
   // G_PTR_ADD to add the negative offset.
   auto Alloc = MIRBuilder.buildSub(IntPtrTy, SPTmp, AllocSize);
-  if (Align) {
-    APInt AlignMask(IntPtrTy.getSizeInBits(), Align, true);
+  if (Alignment > Align(1)) {
+    APInt AlignMask(IntPtrTy.getSizeInBits(), Alignment.value(), true);
     AlignMask.negate();
     auto AlignCst = MIRBuilder.buildConstant(IntPtrTy, AlignMask);
     Alloc = MIRBuilder.buildAnd(IntPtrTy, Alloc, AlignCst);