diff --git a/dlls/ntdll/ntdll.spec b/dlls/ntdll/ntdll.spec
index 8e0058df7c7..269df8f47a4 100644
--- a/dlls/ntdll/ntdll.spec
+++ b/dlls/ntdll/ntdll.spec
@@ -503,7 +503,7 @@
 @ stub RtlDebugPrintTimes
 @ stdcall RtlDecodePointer(ptr)
 # @ stub RtlDecodeSystemPointer
-@ stub RtlDecompressBuffer
+@ stdcall RtlDecompressBuffer(long ptr long ptr long ptr)
 @ stub RtlDecompressFragment
 @ stub RtlDefaultNpAcl
 @ stub RtlDelete
diff --git a/dlls/ntdll/rtl.c b/dlls/ntdll/rtl.c
index 3f2f27e2883..f84c7c4fb2c 100644
--- a/dlls/ntdll/rtl.c
+++ b/dlls/ntdll/rtl.c
@@ -1095,3 +1095,16 @@ NTSTATUS WINAPI RtlCompressBuffer(USHORT CompressionFormatAndEngine, PUCHAR Unco
 
     return STATUS_NOT_IMPLEMENTED;
 }
+
+/******************************************************************************
+ *  RtlDecompressBuffer		[NTDLL.@]
+ */
+NTSTATUS WINAPI RtlDecompressBuffer(USHORT CompressionFormat, PUCHAR UncompressedBuffer,
+                                    ULONG UncompressedBufferSize, PUCHAR CompressedBuffer,
+                                    ULONG CompressedBufferSize, PULONG FinalUncompressedSize)
+{
+    FIXME("0x%04x, %p, %u, %p, %u, %p :stub\n", CompressionFormat, UncompressedBuffer, UncompressedBufferSize,
+         CompressedBuffer, CompressedBufferSize, FinalUncompressedSize);
+
+    return STATUS_NOT_IMPLEMENTED;
+}
diff --git a/include/winternl.h b/include/winternl.h
index 5a014f4e8f3..1a11469bccc 100644
--- a/include/winternl.h
+++ b/include/winternl.h
@@ -2274,6 +2274,7 @@ NTSYSAPI BOOLEAN   WINAPI RtlCreateUnicodeString(PUNICODE_STRING,LPCWSTR);
 NTSYSAPI BOOLEAN   WINAPI RtlCreateUnicodeStringFromAsciiz(PUNICODE_STRING,LPCSTR);
 NTSYSAPI NTSTATUS  WINAPI RtlCreateUserThread(HANDLE,const SECURITY_DESCRIPTOR*,BOOLEAN,PVOID,SIZE_T,SIZE_T,PRTL_THREAD_START_ROUTINE,void*,HANDLE*,CLIENT_ID*);
 NTSYSAPI void      WINAPI RtlDeactivateActivationContext(DWORD,ULONG_PTR);
+NTSYSAPI NTSTATUS  WINAPI RtlDecompressBuffer(USHORT,PUCHAR,ULONG,PUCHAR,ULONG,PULONG);
 NTSYSAPI NTSTATUS  WINAPI RtlDeleteAce(PACL,DWORD);
 NTSYSAPI NTSTATUS  WINAPI RtlDeleteAtomFromAtomTable(RTL_ATOM_TABLE,RTL_ATOM);
 NTSYSAPI NTSTATUS  WINAPI RtlDeleteCriticalSection(RTL_CRITICAL_SECTION *);