diff --git a/verilog/transform/obfuscate.cc b/verilog/transform/obfuscate.cc
index 5984ebb68..cb00cc7bd 100644
--- a/verilog/transform/obfuscate.cc
+++ b/verilog/transform/obfuscate.cc
@@ -47,9 +47,13 @@ static void ObfuscateVerilogCodeInternal(absl::string_view content,
       case verilog_tokentype::PP_Identifier:
         *output << (*subst)(token.text);
         break;
+        // Preserve all $ID calls, including system task/function calls, and VPI
+        // calls
+      case verilog_tokentype::SystemTFIdentifier:
+        *output << token.text;
+        break;
         // The following identifier types start with a special character that
         // needs to be preserved.
-      case verilog_tokentype::SystemTFIdentifier:
       case verilog_tokentype::MacroIdentifier:
       case verilog_tokentype::MacroCallId:
         // TODO(fangism): verilog_tokentype::EscapedIdentifier
diff --git a/verilog/transform/obfuscate_test.cc b/verilog/transform/obfuscate_test.cc
index 1b9718f41..851627b6e 100644
--- a/verilog/transform/obfuscate_test.cc
+++ b/verilog/transform/obfuscate_test.cc
@@ -53,10 +53,10 @@ TEST(ObfuscateVerilogCodeTest, PreloadedSubstitutions) {
        "`ifdef AAA\n`elsif CCC\n`else\n`endif\n"},
       {"`define ccc bbb+aaa\n", "`define CCC BBB+AAA\n"},
       {"`define ccc `bbb+`aaa\n", "`define CCC `BBB+`AAA\n"},
-      {"task bbb;\n  $aaa;\nendtask\n", "task BBB;\n  $AAA;\nendtask\n"},
-      {"task bbb;\n  $aaa();\nendtask\n", "task BBB;\n  $AAA();\nendtask\n"},
+      {"task bbb;\n  $aaa;\nendtask\n", "task BBB;\n  $aaa;\nendtask\n"},
+      {"task bbb;\n  $aaa();\nendtask\n", "task BBB;\n  $aaa();\nendtask\n"},
       {"task bbb;\n  $aaa($ccc());\nendtask\n",
-       "task BBB;\n  $AAA($CCC());\nendtask\n"},
+       "task BBB;\n  $aaa($ccc());\nendtask\n"},
       {"function aaa()\nreturn bbb^ccc;\nendfunction\n",
        "function AAA()\nreturn BBB^CCC;\nendfunction\n"},
       {"function aaa()\nreturn bbb(ccc);\nendfunction\n",