diff --git a/llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp b/llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
--- a/llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
+++ b/llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
@@ -564,6 +564,10 @@
     if (IsWin64CC) {
       GPRIdx = MFI.CreateFixedObject(GPRSaveSize,
                                      -static_cast<int>(GPRSaveSize), false);
+      if (GPRSaveSize & 15)
+        // The extra size here, if triggered, will always be 8.
+        MFI.CreateFixedObject(16 - (GPRSaveSize & 15),
+                              -(int)alignTo(GPRSaveSize, 16), false);
     } else
       GPRIdx = MFI.CreateStackObject(GPRSaveSize, Align(8), false);
 
diff --git a/llvm/test/CodeGen/AArch64/win64_vararg2.ll b/llvm/test/CodeGen/AArch64/win64_vararg2.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/win64_vararg2.ll
@@ -0,0 +1,87 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=aarch64-pc-win32 | FileCheck %s
+; RUN: llc < %s -global-isel -mtriple=aarch64-pc-win32 | FileCheck %s --check-prefix=GISEL
+
+%"struct.std::__1::integral_constant" = type { i8 }
+
+; Function Attrs: mustprogress noinline nounwind optnone uwtable
+define dso_local noundef i1 @_Z8_fits_inIcjNSt3__114numeric_limitsIcEEEbT0_NS0_17integral_constantIbLb0EEES5_z(i32 noundef %0, i8 %1, i8 %2, ...) {
+; CHECK-LABEL: _Z8_fits_inIcjNSt3__114numeric_limitsIcEEEbT0_NS0_17integral_constantIbLb0EEES5_z:
+; CHECK:       .seh_proc _Z8_fits_inIcjNSt3__114numeric_limitsIcEEEbT0_NS0_17integral_constantIbLb0EEES5_z
+; CHECK-NEXT:  // %bb.0:
+; CHECK-NEXT:    sub sp, sp, #80
+; CHECK-NEXT:    .seh_stackalloc 80
+; CHECK-NEXT:    str x19, [sp, #16] // 8-byte Folded Spill
+; CHECK-NEXT:    .seh_save_reg x19, 16
+; CHECK-NEXT:    str x30, [sp, #24] // 8-byte Folded Spill
+; CHECK-NEXT:    .seh_save_reg x30, 24
+; CHECK-NEXT:    .seh_endprologue
+; CHECK-NEXT:    mov w19, w0
+; CHECK-NEXT:    stp x3, x4, [sp, #40]
+; CHECK-NEXT:    stp x5, x6, [sp, #56]
+; CHECK-NEXT:    str x7, [sp, #72]
+; CHECK-NEXT:    strb w1, [sp, #15]
+; CHECK-NEXT:    strb w2, [sp, #14]
+; CHECK-NEXT:    str w0, [sp, #8]
+; CHECK-NEXT:    bl _ZNSt3__114numeric_limitsIcE3maxB7v180000Ev
+; CHECK-NEXT:    cmp w19, w0, uxtb
+; CHECK-NEXT:    cset w0, ls
+; CHECK-NEXT:    .seh_startepilogue
+; CHECK-NEXT:    ldr x30, [sp, #24] // 8-byte Folded Reload
+; CHECK-NEXT:    .seh_save_reg x30, 24
+; CHECK-NEXT:    ldr x19, [sp, #16] // 8-byte Folded Reload
+; CHECK-NEXT:    .seh_save_reg x19, 16
+; CHECK-NEXT:    add sp, sp, #80
+; CHECK-NEXT:    .seh_stackalloc 80
+; CHECK-NEXT:    .seh_endepilogue
+; CHECK-NEXT:    ret
+; CHECK-NEXT:    .seh_endfunclet
+; CHECK-NEXT:    .seh_endproc
+;
+; GISEL-LABEL: _Z8_fits_inIcjNSt3__114numeric_limitsIcEEEbT0_NS0_17integral_constantIbLb0EEES5_z:
+; GISEL:       .seh_proc _Z8_fits_inIcjNSt3__114numeric_limitsIcEEEbT0_NS0_17integral_constantIbLb0EEES5_z
+; GISEL-NEXT:  // %bb.0:
+; GISEL-NEXT:    sub sp, sp, #80
+; GISEL-NEXT:    .seh_stackalloc 80
+; GISEL-NEXT:    str x19, [sp, #16] // 8-byte Folded Spill
+; GISEL-NEXT:    .seh_save_reg x19, 16
+; GISEL-NEXT:    str x30, [sp, #24] // 8-byte Folded Spill
+; GISEL-NEXT:    .seh_save_reg x30, 24
+; GISEL-NEXT:    .seh_endprologue
+; GISEL-NEXT:    stp x3, x4, [sp, #40]
+; GISEL-NEXT:    mov w19, w0
+; GISEL-NEXT:    stp x5, x6, [sp, #56]
+; GISEL-NEXT:    str w0, [sp, #8]
+; GISEL-NEXT:    str x7, [sp, #72]
+; GISEL-NEXT:    strb w1, [sp, #15]
+; GISEL-NEXT:    strb w2, [sp, #14]
+; GISEL-NEXT:    bl _ZNSt3__114numeric_limitsIcE3maxB7v180000Ev
+; GISEL-NEXT:    cmp w19, w0, uxtb
+; GISEL-NEXT:    cset w0, ls
+; GISEL-NEXT:    .seh_startepilogue
+; GISEL-NEXT:    ldr x30, [sp, #24] // 8-byte Folded Reload
+; GISEL-NEXT:    .seh_save_reg x30, 24
+; GISEL-NEXT:    ldr x19, [sp, #16] // 8-byte Folded Reload
+; GISEL-NEXT:    .seh_save_reg x19, 16
+; GISEL-NEXT:    add sp, sp, #80
+; GISEL-NEXT:    .seh_stackalloc 80
+; GISEL-NEXT:    .seh_endepilogue
+; GISEL-NEXT:    ret
+; GISEL-NEXT:    .seh_endfunclet
+; GISEL-NEXT:    .seh_endproc
+  %4 = alloca %"struct.std::__1::integral_constant", align 1
+  %5 = alloca %"struct.std::__1::integral_constant", align 1
+  %6 = alloca i32, align 4
+  %7 = getelementptr inbounds %"struct.std::__1::integral_constant", ptr %4, i32 0, i32 0
+  store i8 %1, ptr %7, align 1
+  %8 = getelementptr inbounds %"struct.std::__1::integral_constant", ptr %5, i32 0, i32 0
+  store i8 %2, ptr %8, align 1
+  store i32 %0, ptr %6, align 4
+  %9 = load i32, ptr %6, align 4
+  %10 = call noundef i8 @_ZNSt3__114numeric_limitsIcE3maxB7v180000Ev()
+  %11 = zext i8 %10 to i32
+  %12 = icmp ule i32 %9, %11
+  ret i1 %12
+}
+
+declare dso_local noundef i8 @_ZNSt3__114numeric_limitsIcE3maxB7v180000Ev()