diff --git a/dlls/ntdll/rtl.c b/dlls/ntdll/rtl.c
index 8bbb6104456..d9e448af4e7 100644
--- a/dlls/ntdll/rtl.c
+++ b/dlls/ntdll/rtl.c
@@ -1224,14 +1224,32 @@ PSLIST_ENTRY WINAPI RtlInterlockedPushListSList(PSLIST_HEADER list, PSLIST_ENTRY
 /******************************************************************************
  *  RtlGetCompressionWorkSpaceSize		[NTDLL.@]
  */
-NTSTATUS WINAPI RtlGetCompressionWorkSpaceSize(USHORT CompressionFormatAndEngine,
-                                               PULONG CompressBufferWorkSpaceSize,
-                                               PULONG CompressFragmentWorkSpaceSize)
+NTSTATUS WINAPI RtlGetCompressionWorkSpaceSize(USHORT format, PULONG compress_workspace,
+                                               PULONG decompress_workspace)
 {
-    FIXME("0x%04x, %p, %p: stub!\n", CompressionFormatAndEngine, CompressBufferWorkSpaceSize,
-         CompressFragmentWorkSpaceSize);
+    FIXME("0x%04x, %p, %p: semi-stub\n", format, compress_workspace, decompress_workspace);
 
-    return STATUS_NOT_IMPLEMENTED;
+    switch (format & ~COMPRESSION_ENGINE_MAXIMUM)
+    {
+        case COMPRESSION_FORMAT_LZNT1:
+            if (compress_workspace)
+            {
+                /* FIXME: The current implementation of RtlCompressBuffer does not use a
+                 * workspace buffer, but Windows applications might expect a nonzero value. */
+                *compress_workspace = 16;
+            }
+            if (decompress_workspace)
+                *decompress_workspace = 0x1000;
+            return STATUS_SUCCESS;
+
+        case COMPRESSION_FORMAT_NONE:
+        case COMPRESSION_FORMAT_DEFAULT:
+            return STATUS_INVALID_PARAMETER;
+
+        default:
+            FIXME("format %u not implemented\n", format);
+            return STATUS_UNSUPPORTED_COMPRESSION;
+    }
 }
 
 /* compress data using LZNT1, currently only a stub */
diff --git a/dlls/ntdll/tests/rtl.c b/dlls/ntdll/tests/rtl.c
index a2e7f6cb130..c6a7023be1f 100644
--- a/dlls/ntdll/tests/rtl.c
+++ b/dlls/ntdll/tests/rtl.c
@@ -1623,14 +1623,10 @@ static void test_RtlCompressBuffer(void)
     compress_workspace = decompress_workspace = 0xdeadbeef;
     status = pRtlGetCompressionWorkSpaceSize(COMPRESSION_FORMAT_LZNT1, &compress_workspace,
                                              &decompress_workspace);
-    todo_wine
     ok(status == STATUS_SUCCESS, "got wrong status 0x%08x\n", status);
     ok(compress_workspace != 0, "got wrong compress_workspace %u\n", compress_workspace);
-    if (status == STATUS_SUCCESS)
-    {
-        workspace = HeapAlloc(GetProcessHeap(), 0, compress_workspace);
-        ok(workspace != NULL, "HeapAlloc failed %d\n", GetLastError());
-    }
+    workspace = HeapAlloc(GetProcessHeap(), 0, compress_workspace);
+    ok(workspace != NULL, "HeapAlloc failed %d\n", GetLastError());
 
     /* test compression format / engine */
     final_size = 0xdeadbeef;
@@ -1699,35 +1695,28 @@ static void test_RtlGetCompressionWorkSpaceSize(void)
     /* test invalid format / engine */
     status = pRtlGetCompressionWorkSpaceSize(COMPRESSION_FORMAT_NONE, &compress_workspace,
                                              &decompress_workspace);
-    todo_wine
     ok(status == STATUS_INVALID_PARAMETER, "got wrong status 0x%08x\n", status);
 
     status = pRtlGetCompressionWorkSpaceSize(COMPRESSION_FORMAT_DEFAULT, &compress_workspace,
                                              &decompress_workspace);
-    todo_wine
     ok(status == STATUS_INVALID_PARAMETER, "got wrong status 0x%08x\n", status);
 
     status = pRtlGetCompressionWorkSpaceSize(0xFF, &compress_workspace, &decompress_workspace);
-    todo_wine
     ok(status == STATUS_UNSUPPORTED_COMPRESSION, "got wrong status 0x%08x\n", status);
 
     /* test LZNT1 with normal and maximum compression */
     compress_workspace = decompress_workspace = 0xdeadbeef;
     status = pRtlGetCompressionWorkSpaceSize(COMPRESSION_FORMAT_LZNT1, &compress_workspace,
                                              &decompress_workspace);
-    todo_wine
     ok(status == STATUS_SUCCESS, "got wrong status 0x%08x\n", status);
     ok(compress_workspace != 0, "got wrong compress_workspace %u\n", compress_workspace);
-    todo_wine
     ok(decompress_workspace == 0x1000, "got wrong decompress_workspace %u\n", decompress_workspace);
 
     compress_workspace = decompress_workspace = 0xdeadbeef;
     status = pRtlGetCompressionWorkSpaceSize(COMPRESSION_FORMAT_LZNT1 | COMPRESSION_ENGINE_MAXIMUM,
                                              &compress_workspace, &decompress_workspace);
-    todo_wine
     ok(status == STATUS_SUCCESS, "got wrong status 0x%08x\n", status);
     ok(compress_workspace != 0, "got wrong compress_workspace %u\n", compress_workspace);
-    todo_wine
     ok(decompress_workspace == 0x1000, "got wrong decompress_workspace %u\n", decompress_workspace);
 }