diff --git a/src/Compiler/lex.fsl b/src/Compiler/lex.fsl
index b3ddfad4a13..995f3fe09c0 100644
--- a/src/Compiler/lex.fsl
+++ b/src/Compiler/lex.fsl
@@ -939,7 +939,9 @@ rule token (args: LexArgs) (skip: bool) = parse
 
  | "-" { MINUS }
 
- | "~" { RESERVED }
+ | "~"
+     { errorR (Error(FSComp.SR.lexInvalidIdentifier(), lexbuf.LexemeRange))
+       RESERVED }
 
  | ignored_op_char* '*' '*'                    op_char* { checkExprOp lexbuf; INFIX_STAR_STAR_OP(lexeme lexbuf) }
 
diff --git a/tests/service/data/SyntaxTree/Expression/Unary - Reserved 01.fs b/tests/service/data/SyntaxTree/Expression/Unary - Reserved 01.fs
new file mode 100644
index 00000000000..474693d2043
--- /dev/null
+++ b/tests/service/data/SyntaxTree/Expression/Unary - Reserved 01.fs	
@@ -0,0 +1,3 @@
+module Module
+
+~x
diff --git a/tests/service/data/SyntaxTree/Expression/Unary - Reserved 01.fs.bsl b/tests/service/data/SyntaxTree/Expression/Unary - Reserved 01.fs.bsl
new file mode 100644
index 00000000000..0ef183357aa
--- /dev/null
+++ b/tests/service/data/SyntaxTree/Expression/Unary - Reserved 01.fs.bsl	
@@ -0,0 +1,17 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Expression/Unary - Reserved 01.fs", false,
+      QualifiedNameOfFile Module, [], [],
+      [SynModuleOrNamespace
+         ([Module], false, NamedModule,
+          [Expr
+             (App
+                (NonAtomic, false,
+                 ArbitraryAfterError ("unfinished identifier", (3,0--3,1)),
+                 Ident x, (3,0--3,2)), (3,0--3,2))],
+          PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector), [], None,
+          (1,0--3,2), { LeadingKeyword = Module (1,0--1,6) })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))
+
+(3,0)-(3,1) parse error This is not a valid identifier
diff --git a/tests/service/data/SyntaxTree/Expression/Unary - Reserved 02.fs b/tests/service/data/SyntaxTree/Expression/Unary - Reserved 02.fs
new file mode 100644
index 00000000000..e848e499d1d
--- /dev/null
+++ b/tests/service/data/SyntaxTree/Expression/Unary - Reserved 02.fs	
@@ -0,0 +1,3 @@
+module Module
+
+x ~ y
diff --git a/tests/service/data/SyntaxTree/Expression/Unary - Reserved 02.fs.bsl b/tests/service/data/SyntaxTree/Expression/Unary - Reserved 02.fs.bsl
new file mode 100644
index 00000000000..d246acbd5b9
--- /dev/null
+++ b/tests/service/data/SyntaxTree/Expression/Unary - Reserved 02.fs.bsl	
@@ -0,0 +1,19 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Expression/Unary - Reserved 02.fs", false,
+      QualifiedNameOfFile Module, [], [],
+      [SynModuleOrNamespace
+         ([Module], false, NamedModule,
+          [Expr
+             (App
+                (NonAtomic, false,
+                 App
+                   (NonAtomic, false, Ident x,
+                    ArbitraryAfterError ("unfinished identifier", (3,2--3,3)),
+                    (3,0--3,3)), Ident y, (3,0--3,5)), (3,0--3,5))],
+          PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector), [], None,
+          (1,0--3,5), { LeadingKeyword = Module (1,0--1,6) })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))
+
+(3,2)-(3,3) parse error This is not a valid identifier