diff --git a/src/fsharp/lex.fsl b/src/fsharp/lex.fsl
index 1fab60bb7ba..89bf263e4ba 100644
--- a/src/fsharp/lex.fsl
+++ b/src/fsharp/lex.fsl
@@ -203,8 +203,8 @@ let xint8 = xinteger 'y'
 let xint16 = xinteger 's'
 let xint = xinteger 
 let xint32 = xinteger 'l'
-let floatp = digit ((digit | separator)* digit)? '.' (digit (digit | separator)*)?  
-let floate = digit ((digit | separator)* digit)? ('.' (digit (digit | separator)*)? )? ('e'| 'E') ['+' '-']? digit (digit | separator)*
+let floatp = digit ((digit | separator)* digit)? '.' (digit ((digit | separator)* digit)?)?  
+let floate = digit ((digit | separator)* digit)? ('.' (digit ((digit | separator)* digit)?)? )? ('e'| 'E') ['+' '-']? digit ((digit | separator)* digit)?
 let float = floatp | floate 
 let bignum =  integer ('I'  | 'N' | 'Z' | 'Q' | 'R' | 'G')
 let ieee64 = float
diff --git a/tests/fsharpqa/Source/Conformance/BasicGrammarElements/Constants/E_UnderscoreLiterals.fs b/tests/fsharpqa/Source/Conformance/BasicGrammarElements/Constants/E_UnderscoreLiterals.fs
new file mode 100644
index 00000000000..6e1ba665f93
--- /dev/null
+++ b/tests/fsharpqa/Source/Conformance/BasicGrammarElements/Constants/E_UnderscoreLiterals.fs
@@ -0,0 +1,32 @@
+//<Expects id="FS1156" span="(18,11-18,13)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(18,14-18,19)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS0599" span="(18,13-18,14)" status="error">Missing qualification after '.'</Expects>
+//<Expects id="FS1156" span="(19,11-19,19)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(20,29-20,42)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(22,10-22,13)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(23,10-23,15)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(24,10-24,15)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(25,10-25,15)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(26,10-26,14)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(27,10-27,15)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(28,10-28,15)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(29,10-29,15)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(30,11-30,18)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(31,11-31,18)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+//<Expects id="FS1156" span="(32,11-32,16)" status="error">This is not a valid numeric literal. Valid numeric literals include</Expects>
+
+let pi1 = 3_.1415F
+let pi2 = 3._1415F
+let socialSecurityNumber1 = 999_99_9999_L
+let x1 = _52
+let x2 = 52_
+let x3 = 0_x52
+let x4 = 0x_52
+let x5 = 0x52_
+let x6 = 052_
+let x7 = 0_o52
+let x8 = 0o_52
+let x9 = 0o52_
+let x10 = 2.1_e2F
+let x11 = 2.1e_2F
+let x12 = 1.0_F
\ No newline at end of file
diff --git a/tests/fsharpqa/Source/Conformance/BasicGrammarElements/Constants/env.lst b/tests/fsharpqa/Source/Conformance/BasicGrammarElements/Constants/env.lst
index 83cd11faab1..500d42d77e1 100644
--- a/tests/fsharpqa/Source/Conformance/BasicGrammarElements/Constants/env.lst
+++ b/tests/fsharpqa/Source/Conformance/BasicGrammarElements/Constants/env.lst
@@ -13,3 +13,4 @@ NOMONO,NoMT	SOURCE=E_BasicConstantsBigNum40.fsx SCFLAGS="--test:ErrorRanges"	# E
 	SOURCE=DecimalLiterals02.fs					# DecimalLiterals02.fs
 
 	SOURCE=FullSetOfEscapeCharacters.fs				# FullSetOfEscapeCharacters.fs
+	SOURCE=E_UnderscoreLiterals.fs SCFLAGS="--test:ErrorRanges"	# E_UnderscoreLiterals.fs
\ No newline at end of file