diff --git a/grammar/src/class_members.grm b/grammar/src/class_members.grm
index 127c85a2d87..30b0e2499e5 100644
--- a/grammar/src/class_members.grm
+++ b/grammar/src/class_members.grm
@@ -55,7 +55,11 @@ super
   ;
 
 method
-  : methodModifier* "fun" SimpleName typeParameters? functionParameters (":" type)? functionBody?
+  : methodModifier* "fun" functionRest
+  ;
+
+functionRest
+  : SimpleName typeParameters? functionParameters (":" type)? functionBody?
   ;
 
 functionParameters
@@ -72,7 +76,10 @@ functionBody
   ;
 
 property
-  : propertyModifier* ("val" | "var") SimpleName (":" type)? ("=" expression)?
+  : propertyModifier* ("val" | "var")
+
+propertyRest
+  : SimpleName (":" type)? ("=" expression)?
     "{" getter? setter? "}"
   ;
 
diff --git a/grammar/src/extension.grm b/grammar/src/extension.grm
new file mode 100644
index 00000000000..fa5449b95ee
--- /dev/null
+++ b/grammar/src/extension.grm
@@ -0,0 +1,17 @@
+extension
+  : completeExtension
+  : extensionMethod
+  : extensionProperty
+  ;
+
+completeExtension
+  : accessModifier? "extension" SimpleName? typeParameters? "for" type classBody?
+  ;
+
+extensionMethod
+  : accessModifier? "extension" "fun" type "." functionRest
+  ;
+
+extensionProperty
+  : accessModifier? "extension" propertyRest
+  ;
diff --git a/grammar/src/toplevel.grm b/grammar/src/toplevel.grm
new file mode 100644
index 00000000000..82fb18100bb
--- /dev/null
+++ b/grammar/src/toplevel.grm
@@ -0,0 +1,14 @@
+jetlFile
+  : preamble toplevelObject*
+  ;
+
+preamble
+  : empty
+  ;
+
+toplevelObject
+  : class
+  : extension
+  : method
+  : property
+  ;
\ No newline at end of file