diff --git a/pkg/front_end/lib/src/fasta/fasta_codes_generated.dart b/pkg/front_end/lib/src/fasta/fasta_codes_generated.dart
index 973ec6e..574152c 100644
--- a/pkg/front_end/lib/src/fasta/fasta_codes_generated.dart
+++ b/pkg/front_end/lib/src/fasta/fasta_codes_generated.dart
@@ -3329,7 +3329,10 @@
 
   -Dname
   -Dname=value
-    Ignored for now.
+    Define an environment variable in the compile-time environment.
+
+  --no-defines
+    Ignore all -D options and leave environment constants unevaluated.
 
   --
     Stop option parsing, the rest of the command line is assumed to be
diff --git a/pkg/front_end/messages.yaml b/pkg/front_end/messages.yaml
index 4c4c0a9..195f967 100644
--- a/pkg/front_end/messages.yaml
+++ b/pkg/front_end/messages.yaml
@@ -1538,7 +1538,10 @@
 
       -Dname
       -Dname=value
-        Ignored for now.
+        Define an environment variable in the compile-time environment.
+
+      --no-defines
+        Ignore all -D options and leave environment constants unevaluated.
 
       --
         Stop option parsing, the rest of the command line is assumed to be
diff --git a/pkg/front_end/tool/_fasta/command_line.dart b/pkg/front_end/tool/_fasta/command_line.dart
index 385d151..ae7650d 100644
--- a/pkg/front_end/tool/_fasta/command_line.dart
+++ b/pkg/front_end/tool/_fasta/command_line.dart
@@ -251,6 +251,7 @@
   "--legacy": "--legacy-mode",
   "--legacy-mode": false,
   "--libraries-json": Uri,
+  "--no-defines": false,
   "--output": Uri,
   "--packages": Uri,
   "--platform": Uri,
@@ -310,6 +311,8 @@
         "Valid targets are:\n  ${targets.keys.join("\n  ")}");
   }
 
+  final bool noDefines = options["--no-defines"];
+
   final bool enableAsserts = options["--enable-asserts"];
 
   final bool verify = options["--verify"];
@@ -385,7 +388,7 @@
           ..verify = verify
           ..bytecode = bytecode
           ..experimentalFlags = experimentalFlags
-          ..environmentDefines = parsedArguments.defines,
+          ..environmentDefines = noDefines ? null : parsedArguments.defines,
         inputs: <Uri>[Uri.parse(arguments[0])],
         output: resolveInputUri(arguments[3]));
   } else if (arguments.isEmpty) {
@@ -421,7 +424,7 @@
     ..verbose = verbose
     ..verify = verify
     ..experimentalFlags = experimentalFlags
-    ..environmentDefines = parsedArguments.defines;
+    ..environmentDefines = noDefines ? null : parsedArguments.defines;
 
   // TODO(ahe): What about chase dependencies?