diff --git a/dll/ntdll/ldr/ldrinit.c b/dll/ntdll/ldr/ldrinit.c
index 991f498dba252..efe3a9ec6085d 100644
--- a/dll/ntdll/ldr/ldrinit.c
+++ b/dll/ntdll/ldr/ldrinit.c
@@ -1538,7 +1538,36 @@ VOID
 NTAPI
 LdrpValidateImageForMp(IN PLDR_DATA_TABLE_ENTRY LdrDataTableEntry)
 {
-    UNIMPLEMENTED;
+    PIMAGE_NT_HEADERS NtHeaders;
+    NTSTATUS Status;
+
+    /* Get the NT Headers */
+    NtHeaders = RtlImageNtHeader(LdrDataTableEntry->DllBase);
+    if (NtHeaders == NULL)
+    {
+        RtlRaiseStatus(STATUS_INVALID_IMAGE_FORMAT);
+    }
+
+    /* Check if the image is UP only */
+    if (NtHeaders->FileHeader.Characteristics & IMAGE_FILE_UP_SYSTEM_ONLY)
+    {
+        /* Set process affinity to 1 */
+        DPRINT1("LDR: Image is UP only, setting process affinity to 1\n");
+        KAFFINITY AffinityMask = 1;
+        Status = NtSetInformationProcess(NtCurrentProcess(),
+                                         ProcessAffinityMask,
+                                         &AffinityMask,
+                                         sizeof(AffinityMask));
+        if (!NT_SUCCESS(Status))
+        {
+            RtlRaiseStatus(Status);
+        }
+
+        /* Save it in the PEB */
+        NtCurrentPeb()->NumberOfProcessors = 1;
+    }
+
+    // FIXME: Anything else to do?
 }
 
 BOOLEAN