diff --git a/dlls/api-ms-win-core-processthreads-l1-1-1/api-ms-win-core-processthreads-l1-1-1.spec b/dlls/api-ms-win-core-processthreads-l1-1-1/api-ms-win-core-processthreads-l1-1-1.spec
index e7e2c02b308..149678995cc 100644
--- a/dlls/api-ms-win-core-processthreads-l1-1-1/api-ms-win-core-processthreads-l1-1-1.spec
+++ b/dlls/api-ms-win-core-processthreads-l1-1-1/api-ms-win-core-processthreads-l1-1-1.spec
@@ -47,7 +47,7 @@
 @ stub SetProcessMitigationPolicy
 @ stdcall SetProcessShutdownParameters(long long) kernel32.SetProcessShutdownParameters
 @ stdcall SetThreadContext(long ptr) kernel32.SetThreadContext
-@ stub SetThreadIdealProcessorEx
+@ stdcall SetThreadIdealProcessorEx(long ptr ptr) kernel32.SetThreadIdealProcessorEx
 @ stdcall SetThreadPriority(long long) kernel32.SetThreadPriority
 @ stdcall SetThreadPriorityBoost(long long) kernel32.SetThreadPriorityBoost
 @ stdcall SetThreadStackGuarantee(ptr) kernel32.SetThreadStackGuarantee
diff --git a/dlls/api-ms-win-core-processthreads-l1-1-2/api-ms-win-core-processthreads-l1-1-2.spec b/dlls/api-ms-win-core-processthreads-l1-1-2/api-ms-win-core-processthreads-l1-1-2.spec
index 968b960a6ae..c902274459e 100644
--- a/dlls/api-ms-win-core-processthreads-l1-1-2/api-ms-win-core-processthreads-l1-1-2.spec
+++ b/dlls/api-ms-win-core-processthreads-l1-1-2/api-ms-win-core-processthreads-l1-1-2.spec
@@ -53,7 +53,7 @@
 @ stdcall SetProcessPriorityBoost(long long) kernel32.SetProcessPriorityBoost
 @ stdcall SetProcessShutdownParameters(long long) kernel32.SetProcessShutdownParameters
 @ stdcall SetThreadContext(long ptr) kernel32.SetThreadContext
-@ stub SetThreadIdealProcessorEx
+@ stdcall SetThreadIdealProcessorEx(long ptr ptr) kernel32.SetThreadIdealProcessorEx
 @ stub SetThreadInformation
 @ stdcall SetThreadPriority(long long) kernel32.SetThreadPriority
 @ stdcall SetThreadPriorityBoost(long long) kernel32.SetThreadPriorityBoost
diff --git a/dlls/kernel32/kernel32.spec b/dlls/kernel32/kernel32.spec
index 3260cdd823c..1a11af579f4 100644
--- a/dlls/kernel32/kernel32.spec
+++ b/dlls/kernel32/kernel32.spec
@@ -1449,7 +1449,7 @@
 @ stdcall SetThreadExecutionState(long)
 @ stdcall SetThreadGroupAffinity(long ptr ptr)
 @ stdcall SetThreadIdealProcessor(long long)
-# @ stub SetThreadIdealProcessorEx
+@ stdcall SetThreadIdealProcessorEx(long ptr ptr)
 @ stdcall SetThreadLocale(long)
 @ stdcall SetThreadPreferredUILanguages(long ptr ptr)
 @ stdcall SetThreadPriority(long long)
diff --git a/dlls/kernel32/thread.c b/dlls/kernel32/thread.c
index de466185e9c..ac2c3687789 100644
--- a/dlls/kernel32/thread.c
+++ b/dlls/kernel32/thread.c
@@ -471,6 +471,15 @@ DWORD WINAPI SetThreadIdealProcessor(
     return 0;
 }
 
+/***********************************************************************
+ *              SetThreadIdealProcessorEx (KERNEL32.@)
+ */
+BOOL SetThreadIdealProcessorEx( HANDLE thread, PROCESSOR_NUMBER *ideal, PROCESSOR_NUMBER *previous )
+{
+    FIXME("(%p %p %p): stub\n", thread, ideal, previous);
+    SetLastError(ERROR_CALL_NOT_IMPLEMENTED);
+    return FALSE;
+}
 
 /***********************************************************************
  *           GetThreadSelectorEntry   (KERNEL32.@)
diff --git a/dlls/kernelbase/kernelbase.spec b/dlls/kernelbase/kernelbase.spec
index 689d58739e6..bb80f212936 100644
--- a/dlls/kernelbase/kernelbase.spec
+++ b/dlls/kernelbase/kernelbase.spec
@@ -1482,7 +1482,7 @@
 @ stdcall SetThreadErrorMode(long ptr) kernel32.SetThreadErrorMode
 @ stdcall SetThreadGroupAffinity(long ptr ptr) kernel32.SetThreadGroupAffinity
 @ stdcall SetThreadIdealProcessor(long long) kernel32.SetThreadIdealProcessor
-# @ stub SetThreadIdealProcessorEx
+@ stdcall SetThreadIdealProcessorEx(long ptr ptr) kernel32.SetThreadIdealProcessorEx
 # @ stub SetThreadInformation
 @ stdcall SetThreadLocale(long) kernel32.SetThreadLocale
 @ stdcall SetThreadPreferredUILanguages(long ptr ptr) kernel32.SetThreadPreferredUILanguages