diff --git a/dlls/ntdll/heap.c b/dlls/ntdll/heap.c
index 4dc3e7296b6..ec4e376bd4b 100644
--- a/dlls/ntdll/heap.c
+++ b/dlls/ntdll/heap.c
@@ -1490,23 +1490,9 @@ static void heap_set_debug_flags( HANDLE handle )
 
 /***********************************************************************
  *           RtlCreateHeap   (NTDLL.@)
- *
- * Create a new Heap.
- *
- * PARAMS
- *  flags      [I] HEAP_ flags from "winnt.h"
- *  addr       [I] Desired base address
- *  totalSize  [I] Total size of the heap, or 0 for a growable heap
- *  commitSize [I] Amount of heap space to commit
- *  unknown    [I] Not yet understood
- *  definition [I] Heap definition
- *
- * RETURNS
- *  Success: A HANDLE to the newly created heap.
- *  Failure: a NULL HANDLE.
  */
 HANDLE WINAPI RtlCreateHeap( ULONG flags, void *addr, SIZE_T total_size, SIZE_T commit_size,
-                             void *unknown, RTL_HEAP_DEFINITION *definition )
+                             void *lock, RTL_HEAP_PARAMETERS *params )
 {
     struct entry *entry;
     struct heap *heap;
@@ -1514,8 +1500,8 @@ HANDLE WINAPI RtlCreateHeap( ULONG flags, void *addr, SIZE_T total_size, SIZE_T
     SUBHEAP *subheap;
     unsigned int i;
 
-    TRACE( "flags %#lx, addr %p, total_size %#Ix, commit_size %#Ix, unknown %p, definition %p\n",
-           flags, addr, total_size, commit_size, unknown, definition );
+    TRACE( "flags %#lx, addr %p, total_size %#Ix, commit_size %#Ix, lock %p, params %p\n",
+           flags, addr, total_size, commit_size, lock, params );
 
     flags &= ~(HEAP_TAIL_CHECKING_ENABLED|HEAP_FREE_CHECKING_ENABLED);
     if (process_heap) flags |= HEAP_PRIVATE;
diff --git a/include/winternl.h b/include/winternl.h
index ff8756211a1..b1687349ff6 100644
--- a/include/winternl.h
+++ b/include/winternl.h
@@ -2577,11 +2577,23 @@ typedef struct _PROCESS_STACK_ALLOCATION_INFORMATION_EX
     PROCESS_STACK_ALLOCATION_INFORMATION AllocInfo;
 } PROCESS_STACK_ALLOCATION_INFORMATION_EX, *PPROCESS_STACK_ALLOCATION_INFORMATION_EX;
 
-typedef struct _RTL_HEAP_DEFINITION {
-    ULONG Length; /* = sizeof(RTL_HEAP_DEFINITION) */
+typedef NTSTATUS (NTAPI RTL_HEAP_COMMIT_ROUTINE)(PVOID base, PVOID *address, PSIZE_T size);
+typedef RTL_HEAP_COMMIT_ROUTINE *PRTL_HEAP_COMMIT_ROUTINE;
 
-    ULONG Unknown[11];
-} RTL_HEAP_DEFINITION, *PRTL_HEAP_DEFINITION;
+typedef struct _RTL_HEAP_PARAMETERS
+{
+    ULONG Length;
+    SIZE_T SegmentReserve;
+    SIZE_T SegmentCommit;
+    SIZE_T DeCommitFreeblockThreshold;
+    SIZE_T DeCommitTotalFreeThreshold;
+    SIZE_T MaximumAllocationSize;
+    SIZE_T VirtualMemoryThreshold;
+    SIZE_T InitialCommit;
+    SIZE_T InitialReserve;
+    PRTL_HEAP_COMMIT_ROUTINE CommitRoutine;
+    SIZE_T Reserved[2];
+} RTL_HEAP_PARAMETERS, *PRTL_HEAP_PARAMETERS;
 
 typedef struct _RTL_RWLOCK {
     RTL_CRITICAL_SECTION rtlCS;
@@ -4665,7 +4677,7 @@ NTSYSAPI NTSTATUS  WINAPI RtlCreateAcl(PACL,DWORD,DWORD);
 NTSYSAPI NTSTATUS  WINAPI RtlCreateActivationContext(HANDLE*,const void*);
 NTSYSAPI NTSTATUS  WINAPI RtlCreateAtomTable(ULONG,RTL_ATOM_TABLE*);
 NTSYSAPI NTSTATUS  WINAPI RtlCreateEnvironment(BOOLEAN, PWSTR*);
-NTSYSAPI HANDLE    WINAPI RtlCreateHeap(ULONG,PVOID,SIZE_T,SIZE_T,PVOID,PRTL_HEAP_DEFINITION);
+NTSYSAPI HANDLE    WINAPI RtlCreateHeap(ULONG,PVOID,SIZE_T,SIZE_T,PVOID,PRTL_HEAP_PARAMETERS);
 NTSYSAPI NTSTATUS  WINAPI RtlCreateProcessParameters(RTL_USER_PROCESS_PARAMETERS**,const UNICODE_STRING*,const UNICODE_STRING*,const UNICODE_STRING*,const UNICODE_STRING*,PWSTR,const UNICODE_STRING*,const UNICODE_STRING*,const UNICODE_STRING*,const UNICODE_STRING*);
 NTSYSAPI NTSTATUS  WINAPI RtlCreateProcessParametersEx(RTL_USER_PROCESS_PARAMETERS**,const UNICODE_STRING*,const UNICODE_STRING*,const UNICODE_STRING*,const UNICODE_STRING*,PWSTR,const UNICODE_STRING*,const UNICODE_STRING*,const UNICODE_STRING*,const UNICODE_STRING*,ULONG);
 NTSYSAPI PDEBUG_BUFFER WINAPI RtlCreateQueryDebugBuffer(ULONG,BOOLEAN);
diff --git a/tools/winapi/win32.api b/tools/winapi/win32.api
index db3c8e7941e..9e40b61654a 100644
--- a/tools/winapi/win32.api
+++ b/tools/winapi/win32.api
@@ -3344,7 +3344,7 @@ POBJECT_ATTRIBUTES
 PPRIVILEGE_SET
 PRTL_BITMAP
 PRTL_BITMAP_RUN
-PRTL_HEAP_DEFINITION
+PRTL_HEAP_PARAMETERS
 PRTL_QUERY_REGISTRY_TABLE
 PRTL_THREAD_START_ROUTINE
 PRTL_USER_PROCESS_PARAMETERS