diff --git a/reactos/base/system/services/config.c b/reactos/base/system/services/config.c
index a5e19b98253..351a2c2079e 100644
--- a/reactos/base/system/services/config.c
+++ b/reactos/base/system/services/config.c
@@ -15,10 +15,6 @@
 #define NDEBUG
 #include <debug.h>
 
-ULONG
-NTAPI
-RtlLengthSecurityDescriptor(
-  _In_ PSECURITY_DESCRIPTOR SecurityDescriptor);
 
 /* FUNCTIONS *****************************************************************/
 
diff --git a/reactos/sdk/include/ndk/rtlfuncs.h b/reactos/sdk/include/ndk/rtlfuncs.h
index a9c413ab8ad..5b593f23efd 100644
--- a/reactos/sdk/include/ndk/rtlfuncs.h
+++ b/reactos/sdk/include/ndk/rtlfuncs.h
@@ -1469,6 +1469,13 @@ ULONG
 NTAPI
 RtlLengthRequiredSid(IN ULONG SubAuthorityCount);
 
+_IRQL_requires_max_(APC_LEVEL)
+NTSYSAPI
+ULONG
+NTAPI
+RtlLengthSecurityDescriptor(
+    _In_ PSECURITY_DESCRIPTOR SecurityDescriptor);
+
 NTSYSAPI
 ULONG
 NTAPI