diff --git a/src/ipc/lowlevel.cr b/src/ipc/lowlevel.cr
index 3ab481f..eb8b282 100644
--- a/src/ipc/lowlevel.cr
+++ b/src/ipc/lowlevel.cr
@@ -16,7 +16,7 @@ lib LibIPC
 		cinfos :   Connection*
 		pollfd :   Pollfd*
 		tx :       Messages
-		size :     LibC::UInt64
+		size :     LibC::UInt64T
 	end
 
 	struct Switching
@@ -39,7 +39,7 @@ lib LibIPC
 	# Messages are stored in lists within the libipc before being sent.
 	struct Messages
 		messages :  Message*
-		size :      LibC::UInt64
+		size :      LibC::UInt64T
 	end
 
 	struct Message
@@ -82,7 +82,7 @@ lib LibIPC
 	fun ipc_connection(Ctx*, LibC::Char*) : IPCError
 
 	# Closing connections.
-	fun ipc_close(ctx : Ctx*, index : LibC::UInt64) : IPCError
+	fun ipc_close(ctx : Ctx*, index : LibC::UInt64T) : IPCError
 	fun ipc_close_all(ctx : Ctx*) # Void
 
 	fun ipc_ctx_free(Ctx*)        # Void