diff --git a/source/slang/slang.cpp b/source/slang/slang.cpp
index a233424581..8dfaf115e8 100644
--- a/source/slang/slang.cpp
+++ b/source/slang/slang.cpp
@@ -2365,7 +2365,7 @@ Dictionary<String, String> TranslationUnitRequest::getCombinedPreprocessorDefini
     // variables.
     {
         // Used to identify level of HLSL language compatibility
-        combinedPreprocessorDefinitions.addIfNotExists("__HLSL_VERSION", "2020");
+        combinedPreprocessorDefinitions.addIfNotExists("__HLSL_VERSION", "2018");
 
         // Indicates this is being compiled by the slang *compiler*
         combinedPreprocessorDefinitions.addIfNotExists("__SLANG_COMPILER__", "1");
diff --git a/tests/preprocessor/simple-pre-defined.hlsl.expected b/tests/preprocessor/simple-pre-defined.hlsl.expected
index 98911f3c70..6634c9cd6f 100644
--- a/tests/preprocessor/simple-pre-defined.hlsl.expected
+++ b/tests/preprocessor/simple-pre-defined.hlsl.expected
@@ -2,5 +2,5 @@ result code = 0
 standard error = {
 }
 standard output = {
-1 2020 0 1 
+1 2018 0 1 
 }
diff --git a/tests/preprocessor/simple-pre-defined.slang.expected b/tests/preprocessor/simple-pre-defined.slang.expected
index 4b5184e74b..5c6991e41d 100644
--- a/tests/preprocessor/simple-pre-defined.slang.expected
+++ b/tests/preprocessor/simple-pre-defined.slang.expected
@@ -2,5 +2,5 @@ result code = 0
 standard error = {
 }
 standard output = {
-1 2020 1 0 
+1 2018 1 0 
 }