diff --git a/spec/std/llvm/x86_64_abi_spec.cr b/spec/std/llvm/x86_64_abi_spec.cr
index 2e2514e209d2..7c0344769aa3 100644
--- a/spec/std/llvm/x86_64_abi_spec.cr
+++ b/spec/std/llvm/x86_64_abi_spec.cr
@@ -144,6 +144,30 @@ class LLVM::ABI
           info.arg_types[0].should eq(ArgType.indirect(str, Attribute::ByVal))
           info.return_type.should eq(ArgType.indirect(str, Attribute::StructRet))
         end
+
+        test "does with packed struct containing unaligned fields (#9873)" do |abi, ctx|
+          str = ctx.struct([ctx.int8, ctx.int16], packed: true)
+          arg_types = [str]
+          return_type = str
+
+          info = abi.abi_info(arg_types, return_type, true, ctx)
+          info.arg_types.size.should eq(1)
+
+          info.arg_types[0].should eq(ArgType.indirect(str, Attribute::ByVal))
+          info.return_type.should eq(ArgType.indirect(str, Attribute::StructRet))
+        end
+
+        test "does with packed struct not containing unaligned fields" do |abi, ctx|
+          str = ctx.struct([ctx.int16, ctx.int8], packed: true)
+          arg_types = [str]
+          return_type = str
+
+          info = abi.abi_info(arg_types, return_type, true, ctx)
+          info.arg_types.size.should eq(1)
+
+          info.arg_types[0].should eq(ArgType.direct(str, cast: ctx.struct([ctx.int64])))
+          info.return_type.should eq(ArgType.direct(str, cast: ctx.struct([ctx.int64])))
+        end
       end
     {% end %}
   end
diff --git a/src/llvm/abi/x86_64.cr b/src/llvm/abi/x86_64.cr
index e1e996f178e7..5dff628655be 100644
--- a/src/llvm/abi/x86_64.cr
+++ b/src/llvm/abi/x86_64.cr
@@ -100,7 +100,7 @@ class LLVM::ABI::X86_64 < LLVM::ABI
   def classify(type)
     words = (size(type) + 7) // 8
     reg_classes = Array.new(words, RegClass::NoClass)
-    if words > 4
+    if words > 4 || has_misaligned_fields?(type)
       all_mem(reg_classes)
     else
       classify(type, reg_classes, 0, 0)
@@ -275,6 +275,16 @@ class LLVM::ABI::X86_64 < LLVM::ABI
     size(type, 8)
   end
 
+  def has_misaligned_fields?(type : Type) : Bool
+    return false unless type.packed_struct?
+    offset = 0
+    type.struct_element_types.each do |elem|
+      return true unless offset.divisible_by?(align(elem))
+      offset += size(elem)
+    end
+    false
+  end
+
   enum RegClass
     NoClass
     Int