diff --git a/src/Fantomas.Tests/DynamicOperatorTests.fs b/src/Fantomas.Tests/DynamicOperatorTests.fs
new file mode 100644
index 0000000000..0776d0627d
--- /dev/null
+++ b/src/Fantomas.Tests/DynamicOperatorTests.fs
@@ -0,0 +1,17 @@
+module Fantomas.Tests.DynamicOperatorTests
+
+open NUnit.Framework
+open FsUnit
+open Fantomas.Tests.TestHelper
+
+[<Test>]
+let ``Keep () when dynamic operator is used``() =
+    formatSourceString false "let memoEquals x = x?(k + 1)" config
+    |> should equal """let memoEquals x = x?(k + 1)
+"""
+
+[<Test>]
+let ``Remove () when dynamic operator is string``() =
+    formatSourceString false "let memoEquals x = x?k" config
+    |> should equal """let memoEquals x = x?k
+"""
diff --git a/src/Fantomas.Tests/Fantomas.Tests.fsproj b/src/Fantomas.Tests/Fantomas.Tests.fsproj
index d1ceb41f01..37fe0c7f0d 100644
--- a/src/Fantomas.Tests/Fantomas.Tests.fsproj
+++ b/src/Fantomas.Tests/Fantomas.Tests.fsproj
@@ -43,6 +43,7 @@
     <Compile Include="NoTrailingSpacesTests.fs" />
     <Compile Include="LazyTests.fs" />
     <Compile Include="LongIdentWithDotsTests.fs" />
+    <Compile Include="DynamicOperatorTests.fs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Fantomas\Fantomas.fsproj" />
diff --git a/src/Fantomas/CodePrinter.fs b/src/Fantomas/CodePrinter.fs
index 57a50a9892..14c48af604 100644
--- a/src/Fantomas/CodePrinter.fs
+++ b/src/Fantomas/CodePrinter.fs
@@ -574,7 +574,13 @@ and genExpr astContext synExpr =
         !- s +> sepSpace +> sepOpenS +> genExpr { astContext with IsNakedRange = true } e 
         +> ifElse (checkBreakForExpr e) (sepNln +> sepCloseSFixed) sepCloseS
     // This supposes to be an infix function, but for some reason it isn't picked up by InfixApps
-    | App(Var "?", e::es) -> genExpr astContext e -- "?" +> col sepSpace es (genExpr astContext)
+    | App(Var "?", e::es) ->
+        match es with
+        | SynExpr.Const(SynConst.String(_,_),_)::_ ->
+            genExpr astContext e -- "?" +> col sepSpace es (genExpr astContext)
+        | _ ->
+            genExpr astContext e -- "?" +> sepOpenT +> col sepSpace es (genExpr astContext) +> sepCloseT
+
     | App(Var "..", [e1; e2]) ->
         let expr = genExpr astContext e1 -- ".." +> genExpr astContext e2
         ifElse astContext.IsNakedRange expr (sepOpenS +> expr +> sepCloseS)