diff --git a/dlls/winecrt0/stub.c b/dlls/winecrt0/stub.c
index 49e179ef7ed..49fd273def2 100644
--- a/dlls/winecrt0/stub.c
+++ b/dlls/winecrt0/stub.c
@@ -23,7 +23,7 @@
 #include "winbase.h"
 #include "wine/exception.h"
 
-void DECLSPEC_HIDDEN __wine_spec_unimplemented_stub( const char *module, const char *function )
+void DECLSPEC_HIDDEN __cdecl __wine_spec_unimplemented_stub( const char *module, const char *function )
 {
     ULONG_PTR args[2];
 
diff --git a/tools/winebuild/import.c b/tools/winebuild/import.c
index 89a845724e2..d8abc9d03cc 100644
--- a/tools/winebuild/import.c
+++ b/tools/winebuild/import.c
@@ -1250,13 +1250,13 @@ void output_stubs( DLLSPEC *spec )
             output( "\tcall %s\n", asm_name("__wine_spec_unimplemented_stub") );
             break;
         case CPU_x86_64:
-            output( "\tsubq $8,%%rsp\n" );
+            output( "\tsubq $0x28,%%rsp\n" );
             output_cfi( ".cfi_adjust_cfa_offset 8" );
-            output( "\tleaq .L__wine_spec_file_name(%%rip),%%rdi\n" );
+            output( "\tleaq .L__wine_spec_file_name(%%rip),%%rcx\n" );
             if (exp_name)
-                output( "leaq .L%s_string(%%rip),%%rsi\n", name );
+                output( "leaq .L%s_string(%%rip),%%rdx\n", name );
             else
-                output( "\tmovq $%d,%%rsi\n", odp->ordinal );
+                output( "\tmovq $%d,%%rdx\n", odp->ordinal );
             output( "\tcall %s\n", asm_name("__wine_spec_unimplemented_stub") );
             break;
         case CPU_ARM: