diff --git a/Source/cmSourceGroupCommand.cxx b/Source/cmSourceGroupCommand.cxx
index 28ad41f3c5..687a3343f6 100644
--- a/Source/cmSourceGroupCommand.cxx
+++ b/Source/cmSourceGroupCommand.cxx
@@ -133,7 +133,7 @@ bool cmSourceGroupCommand(std::vector<std::string> const& args,
     cm::optional<std::string> Regex;
     cm::optional<ArgumentParser::MaybeEmpty<std::vector<std::string>>>
       FileSets;
-    cm::optional<ArgumentParser::NonEmpty<std::string>> Tree;
+    cm::optional<ArgumentParser::MaybeEmpty<std::string>> Tree;
     cm::optional<ArgumentParser::MaybeEmpty<std::string>> Prefix;
 
     std::map<std::string, std::set<std::string>> FileSetsPerTarget;
diff --git a/Tests/RunCMake/SourceGroup/EmptyTREE.cmake b/Tests/RunCMake/SourceGroup/EmptyTREE.cmake
new file mode 100644
index 0000000000..882ae7c75c
--- /dev/null
+++ b/Tests/RunCMake/SourceGroup/EmptyTREE.cmake
@@ -0,0 +1,2 @@
+
+source_group(TREE "" FILES)
diff --git a/Tests/RunCMake/SourceGroup/RunCMakeTest.cmake b/Tests/RunCMake/SourceGroup/RunCMakeTest.cmake
index 304153cb2f..b4b171b499 100644
--- a/Tests/RunCMake/SourceGroup/RunCMakeTest.cmake
+++ b/Tests/RunCMake/SourceGroup/RunCMakeTest.cmake
@@ -2,6 +2,7 @@
 include(RunCMake)
 
 run_cmake(MixedSignatures)
+run_cmake(EmptyTREE)
 run_cmake(WrongRegex)
 run_cmake(IgnoredKeywords)
 run_cmake(MissingFILE_SETS)