diff --git a/src/crystal/system/win32/iocp.cr b/src/crystal/system/win32/iocp.cr
index b571ca931ecb..374be0a929d3 100644
--- a/src/crystal/system/win32/iocp.cr
+++ b/src/crystal/system/win32/iocp.cr
@@ -9,46 +9,45 @@ struct Crystal::System::IOCP
   @@wait_completion_packet_methods : Bool? = nil
 
   {% if flag?(:interpreted) %}
-    # The interpreter doesn't like the interpreted code to dynamically load
-    # symbols from an external library. We thus merely check for their existence
-    # then simply call them, so the interpreter will load/call them properly.
-    def self.wait_completion_packet_methods? : Bool
-      unless (supported = @@wait_completion_packet_methods).nil?
-        return supported
-      end
-      handle = LibC.LoadLibraryExW(Crystal::System.to_wstr("ntdll.dll"), nil, 0)
-      return @@wait_completion_packet_methods = false if handle.null?
-
-      pointer = LibC.GetProcAddress(handle, "NtCreateWaitCompletionPacket")
-      return @@wait_completion_packet_methods = false if pointer.null?
+    # We can't load the symbols from interpreted code since it would create
+    # interpreted Proc. We thus merely check for the existence of the symbols,
+    # then let the interpreter load the symbols, which will create interpreter
+    # Proc (not interpreted) that can be called.
+    class_getter?(wait_completion_packet_methods : Bool) do
+      detect_wait_completion_packet_symbols
+    end
 
-      @@wait_completion_packet_methods = true
+    private def self.detect_wait_completion_packet_methods : Bool
+      if handle = LibC.LoadLibraryExW(Crystal::System.to_wstr("ntdll.dll"), nil, 0)
+        !LibC.GetProcAddress(handle, "NtCreateWaitCompletionPacket").null?
+      else
+        false
+      end
     end
   {% else %}
-    @@wait_completion_packet_methods : Bool? = nil
-    @@_NtCreateWaitCompletionPacket = uninitialized Proc(LibC::HANDLE*, LibNTDLL::ACCESS_MASK, LibC::OBJECT_ATTRIBUTES*, LibNTDLL::NTSTATUS)
-    @@_NtAssociateWaitCompletionPacket = uninitialized Proc(LibC::HANDLE, LibC::HANDLE, LibC::HANDLE, Void*, Void*, LibNTDLL::NTSTATUS, LibC::ULONG*, LibC::BOOLEAN*, LibNTDLL::NTSTATUS)
-    @@_NtCancelWaitCompletionPacket = uninitialized Proc(LibC::HANDLE, LibC::BOOLEAN, LibNTDLL::NTSTATUS)
-
-    def self.wait_completion_packet_methods? : Bool
-      unless (supported = @@wait_completion_packet_methods).nil?
-        return supported
-      end
+    @@_NtCreateWaitCompletionPacket = uninitialized LibNTDLL::NtCreateWaitCompletionPacketProc
+    @@_NtAssociateWaitCompletionPacket = uninitialized LibNTDLL::NtAssociateWaitCompletionPacketProc
+    @@_NtCancelWaitCompletionPacket = uninitialized LibNTDLL::NtCancelWaitCompletionPacketProc
 
+    class_getter?(wait_completion_packet_methods : Bool) do
+      load_wait_completion_packet_symbols
+    end
+
+    private def self.load_wait_completion_packet_methods : Bool
       handle = LibC.LoadLibraryExW(Crystal::System.to_wstr("ntdll.dll"), nil, 0)
-      return @@wait_completion_packet_methods = false if handle.null?
+      return false if handle.null?
 
       pointer = LibC.GetProcAddress(handle, "NtCreateWaitCompletionPacket")
-      return @@wait_completion_packet_methods = false if pointer.null?
-      @@_NtCreateWaitCompletionPacket = Proc(LibC::HANDLE*, LibNTDLL::ACCESS_MASK, LibC::OBJECT_ATTRIBUTES*, LibNTDLL::NTSTATUS).new(pointer, Pointer(Void).null)
+      return false if pointer.null?
+      @@_NtCreateWaitCompletionPacket = LibNTDLL::NtCreateWaitCompletionPacketProc.new(pointer, Pointer(Void).null)
 
       pointer = LibC.GetProcAddress(handle, "NtAssociateWaitCompletionPacket")
-      @@_NtAssociateWaitCompletionPacket = Proc(LibC::HANDLE, LibC::HANDLE, LibC::HANDLE, Void*, Void*, LibNTDLL::NTSTATUS, LibC::ULONG*, LibC::BOOLEAN*, LibNTDLL::NTSTATUS).new(pointer, Pointer(Void).null)
+      @@_NtAssociateWaitCompletionPacket = LibNTDLL::NtAssociateWaitCompletionPacketProc.new(pointer, Pointer(Void).null)
 
       pointer = LibC.GetProcAddress(handle, "NtCancelWaitCompletionPacket")
-      @@_NtCancelWaitCompletionPacket = Proc(LibC::HANDLE, LibC::BOOLEAN, LibNTDLL::NTSTATUS).new(pointer, Pointer(Void).null)
+      @@_NtCancelWaitCompletionPacket = LibNTDLL::NtCancelWaitCompletionPacketProc.new(pointer, Pointer(Void).null)
 
-      @@wait_completion_packet_methods = true
+      true
     end
   {% end %}
 
diff --git a/src/lib_c/x86_64-windows-msvc/c/ntdll.cr b/src/lib_c/x86_64-windows-msvc/c/ntdll.cr
index 44c1167daf1b..8d2653b8bb31 100644
--- a/src/lib_c/x86_64-windows-msvc/c/ntdll.cr
+++ b/src/lib_c/x86_64-windows-msvc/c/ntdll.cr
@@ -8,6 +8,10 @@ lib LibNTDLL
 
   GENERIC_ALL = 0x10000000_u32
 
+  alias NtCreateWaitCompletionPacketProc = Proc(LibC::HANDLE*, ACCESS_MASK, LibC::OBJECT_ATTRIBUTES*, NTSTATUS)
+  alias NtAssociateWaitCompletionPacketProc = Proc(LibC::HANDLE, LibC::HANDLE, LibC::HANDLE, Void*, Void*, NTSTATUS, LibC::ULONG*, LibC::BOOLEAN*, NTSTATUS)
+  alias NtCancelWaitCompletionPacketProc = Proc(LibC::HANDLE, LibC::BOOLEAN, NTSTATUS)
+
   fun NtCreateWaitCompletionPacket(
     waitCompletionPacketHandle : LibC::HANDLE*,
     desiredAccess : ACCESS_MASK,