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
@@ -74,8 +74,16 @@
     default:
       MIRBuilder.buildCopy(ValVReg, PhysReg);
       break;
+    case CCValAssign::LocInfo::ZExt: {
+      auto WideTy = LLT{VA.getLocVT()};
+      auto NarrowTy = MRI.getType(ValVReg);
+      MIRBuilder.buildTrunc(ValVReg,
+                            MIRBuilder.buildAssertZExt(
+                                WideTy, MIRBuilder.buildCopy(WideTy, PhysReg),
+                                NarrowTy.getSizeInBits()));
+      break;
+    }
     case CCValAssign::LocInfo::SExt:
-    case CCValAssign::LocInfo::ZExt:
     case CCValAssign::LocInfo::AExt: {
       auto Copy = MIRBuilder.buildCopy(LLT{VA.getLocVT()}, PhysReg);
       MIRBuilder.buildTrunc(ValVReg, Copy);
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/call-lowering-zeroext.ll b/llvm/test/CodeGen/AArch64/GlobalISel/call-lowering-zeroext.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/call-lowering-zeroext.ll
@@ -0,0 +1,40 @@
+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+; RUN: llc -mtriple=aarch64 -global-isel -stop-after=irtranslator -verify-machineinstrs -o - %s | FileCheck %s
+
+; Verify that we generate G_ASSERT_ZEXT for zeroext parameters.
+
+define i8 @zeroext_param_i8(i8 zeroext %x) {
+  ; CHECK-LABEL: name: zeroext_param_i8
+  ; CHECK: bb.1 (%ir-block.0):
+  ; CHECK:   liveins: $w0
+  ; CHECK:   [[COPY:%[0-9]+]]:_(s32) = COPY $w0
+  ; CHECK:   [[ASSERT_ZEXT:%[0-9]+]]:_(s32) = G_ASSERT_ZEXT [[COPY]], 8
+  ; CHECK:   [[TRUNC:%[0-9]+]]:_(s8) = G_TRUNC [[ASSERT_ZEXT]](s32)
+  ; CHECK:   [[ANYEXT:%[0-9]+]]:_(s32) = G_ANYEXT [[TRUNC]](s8)
+  ; CHECK:   $w0 = COPY [[ANYEXT]](s32)
+  ; CHECK:   RET_ReallyLR implicit $w0
+  ret i8 %x
+}
+
+define i8 @no_zeroext_param(i8 %x) {
+  ; CHECK-LABEL: name: no_zeroext_param
+  ; CHECK: bb.1 (%ir-block.0):
+  ; CHECK:   liveins: $w0
+  ; CHECK:   [[COPY:%[0-9]+]]:_(s32) = COPY $w0
+  ; CHECK:   [[TRUNC:%[0-9]+]]:_(s8) = G_TRUNC [[COPY]](s32)
+  ; CHECK:   [[ANYEXT:%[0-9]+]]:_(s32) = G_ANYEXT [[TRUNC]](s8)
+  ; CHECK:   $w0 = COPY [[ANYEXT]](s32)
+  ; CHECK:   RET_ReallyLR implicit $w0
+  ret i8 %x
+}
+
+; Don't need G_ASSERT_ZEXT here. The sizes match.
+define i32 @zeroext_param_i32(i32 zeroext %x) {
+  ; CHECK-LABEL: name: zeroext_param_i32
+  ; CHECK: bb.1 (%ir-block.0):
+  ; CHECK:   liveins: $w0
+  ; CHECK:   [[COPY:%[0-9]+]]:_(s32) = COPY $w0
+  ; CHECK:   $w0 = COPY [[COPY]](s32)
+  ; CHECK:   RET_ReallyLR implicit $w0
+  ret i32 %x
+}