diff --git a/lib/stdlib/src/erl_scan.erl b/lib/stdlib/src/erl_scan.erl
index 5b4893b4313b..d70317fe1c35 100644
--- a/lib/stdlib/src/erl_scan.erl
+++ b/lib/stdlib/src/erl_scan.erl
@@ -447,6 +447,15 @@ string_quote(_)    -> $". %"
         (is_integer(C) andalso
          (C >= $\000 andalso C =< $\s orelse C >= $\200 andalso C =< $\240))).
 -define(DIGIT(C), (is_integer(C) andalso $0 =< C andalso C =< $9)).
+-define(NAMECHAR(C),
+        (is_integer(C) andalso
+         (C >= $a andalso C =< $z orelse
+          C >= $A andalso C =< $Z orelse
+          C =:= $_ orelse
+          C >= $0 andalso C =< $9 orelse
+          C =:= $@ orelse
+          C >= $ß andalso C =< $ÿ andalso C =/= $÷ andalso
+          C >= $À andalso C =< $Þ andalso C =/= $×))).
 -define(CHAR(C), (is_integer(C) andalso 0 =< C andalso C < 16#110000)).
 -define(UNICODE(C),
         (is_integer(C) andalso
@@ -1802,6 +1811,8 @@ scan_number([$_]=Cs, St, Line, Col, Toks, Ncs, Us) ->
     {more,{Cs,St,Col,Toks,Line,{Ncs,Us},fun scan_number/6}};
 scan_number([$.,C|Cs], St, Line, Col, Toks, Ncs, Us) when ?DIGIT(C) ->
     scan_fraction(Cs, St, Line, Col, Toks, [C,$.|Ncs], Us);
+scan_number([$.,C|_]=Cs0, _St, Line, Col, _Toks, Ncs, _Us) when ?NAMECHAR(C) ->
+    scan_error({illegal,float}, Line, Col, Line, incr_column(Col, length(Ncs)), Cs0);
 scan_number([$.]=Cs, St, Line, Col, Toks, Ncs, Us) ->
     {more,{Cs,St,Col,Toks,Line,{Ncs,Us},fun scan_number/6}};
 scan_number([$#|Cs]=Cs0, St, Line, Col, Toks, Ncs0, Us) ->
@@ -1818,6 +1829,8 @@ scan_number([$#|Cs]=Cs0, St, Line, Col, Toks, Ncs0, Us) ->
             %% Extremely unlikely to occur in practice.
             scan_error({illegal,base}, Line, Col, Line, Col, Cs0)
     end;
+scan_number([C|_]=Cs0, _St, Line, Col, _Toks, Ncs, _Us) when ?NAMECHAR(C) ->
+    scan_error({illegal,integer}, Line, Col, Line, incr_column(Col, length(Ncs)), Cs0);
 scan_number([]=Cs, St, Line, Col, Toks, Ncs, Us) ->
     {more,{Cs,St,Col,Toks,Line,{Ncs,Us},fun scan_number/6}};
 scan_number(Cs, St, Line, Col, Toks, Ncs0, Us) ->
@@ -1857,6 +1870,8 @@ scan_based_int([$_,Next|Cs], St, Line, Col, Toks, B, [Prev|_]=Ncs, Bcs, _Us)
                    with_underscore);
 scan_based_int([$_]=Cs, St, Line, Col, Toks, B, NCs, BCs, Us) ->
     {more,{Cs,St,Col,Toks,Line,{B,NCs,BCs,Us},fun scan_based_int/6}};
+scan_based_int([C|_]=Cs0, _St, Line, Col, _Toks, _B, Ncs, Bcs, _Us) when ?NAMECHAR(C) ->
+    scan_error({illegal,integer}, Line, Col, Line, incr_column(Col, length(Ncs) + length(Bcs)), Cs0);
 scan_based_int([]=Cs, St, Line, Col, Toks, B, NCs, BCs, Us) ->
     {more,{Cs,St,Col,Toks,Line,{B,NCs,BCs,Us},fun scan_based_int/6}};
 scan_based_int(Cs, _St, Line, Col, _Toks, _B, [], Bcs, _Us) ->
@@ -1889,6 +1904,8 @@ scan_fraction([$_]=Cs, St, Line, Col, Toks, Ncs, Us) ->
     {more,{Cs,St,Col,Toks,Line,{Ncs,Us},fun scan_fraction/6}};
 scan_fraction([E|Cs], St, Line, Col, Toks, Ncs, Us) when E =:= $e; E =:= $E ->
     scan_exponent_sign(Cs, St, Line, Col, Toks, [E|Ncs], Us);
+scan_fraction([C|_]=Cs0, _St, Line, Col, _Toks, Ncs, _Us) when ?NAMECHAR(C) ->
+    scan_error({illegal,float}, Line, Col, Line, incr_column(Col, length(Ncs)), Cs0);
 scan_fraction([]=Cs, St, Line, Col, Toks, Ncs, Us) ->
     {more,{Cs,St,Col,Toks,Line,{Ncs,Us},fun scan_fraction/6}};
 scan_fraction(Cs, St, Line, Col, Toks, Ncs, Us) ->
@@ -1915,6 +1932,8 @@ scan_exponent([$_,Next|Cs], St, Line, Col, Toks, [Prev|_]=Ncs, _) when
     scan_exponent(Cs, St, Line, Col, Toks, [Next,$_|Ncs], with_underscore);
 scan_exponent([$_]=Cs, St, Line, Col, Toks, Ncs, Us) ->
     {more,{Cs,St,Col,Toks,Line,{Ncs,Us},fun scan_exponent/6}};
+scan_exponent([C|_]=Cs0, _St, Line, Col, _Toks, Ncs, _Us) when ?NAMECHAR(C) ->
+    scan_error({illegal,float}, Line, Col, Line, incr_column(Col, length(Ncs)), Cs0);
 scan_exponent([]=Cs, St, Line, Col, Toks, Ncs, Us) ->
     {more,{Cs,St,Col,Toks,Line,{Ncs,Us},fun scan_exponent/6}};
 scan_exponent(Cs, St, Line, Col, Toks, Ncs, Us) ->
diff --git a/lib/stdlib/test/erl_scan_SUITE.erl b/lib/stdlib/test/erl_scan_SUITE.erl
index 28a67b28075c..64577554deaa 100644
--- a/lib/stdlib/test/erl_scan_SUITE.erl
+++ b/lib/stdlib/test/erl_scan_SUITE.erl
@@ -313,24 +313,37 @@ integers() ->
          fun({S, I}) ->
                  test_string(S, [{integer, {1, 1}, I}])
          end, UnderscoreSamples),
-    UnderscoreErrors =
-        ["123_",
-         "123__",
-         "123_456_",
-         "123__456",
-         "_123",
+    NotIntegers =
+        ["_123",
          "__123"],
     lists:foreach(
       fun(S) ->
               case erl_scan:string(S) of
                   {ok, [{integer, _, _}|_], _} ->
                       error({unexpected_integer, S});
-                  _ ->
+                  {ok, _, _} ->
                       ok
               end
-      end, UnderscoreErrors),
-    test_string("_123", [{var,{1,1},'_123'}]),
-    test_string("123_", [{integer,{1,1},123},{var,{1,4},'_'}]),
+      end, NotIntegers),
+    IntegerErrors =
+        ["123_",
+         "123__",
+         "123_456_",
+         "123__456",
+         "123_.456",
+         "123abc",
+         "12@"],
+    lists:foreach(
+      fun(S) ->
+              case erl_scan:string(S) of
+                  {error,{1,erl_scan,{illegal,integer}},_} ->
+                      ok;
+                  {error,Err,_} ->
+                      error({unexpected_error, S, Err});
+                  Succ ->
+                      error({unexpected_success, S, Succ})
+              end
+      end, IntegerErrors),
     ok.
 
 base_integers() ->
@@ -350,8 +363,6 @@ base_integers() ->
     {error,{{1,1},erl_scan,{base,1000}},{1,6}} =
         erl_scan:string("1_000#000", {1,1}, []),
 
-    test_string("12#bc", [{integer,{1,1},11},{atom,{1,5},c}]),
-
     [begin
          Str = BS ++ "#" ++ S,
          E = 2 + length(BS),
@@ -360,12 +371,6 @@ base_integers() ->
      end || {BS,S} <- [{"3","3"},{"15","f"},{"12","c"},
                        {"1_5","f"},{"1_2","c"}] ],
 
-    {ok,[{integer,1,239},{'@',1}],1} = erl_scan_string("16#ef@"),
-    {ok,[{integer,{1,1},239},{'@',{1,6}}],{1,7}} =
-        erl_scan_string("16#ef@", {1,1}, []),
-    {ok,[{integer,{1,1},14},{atom,{1,5},g@}],{1,7}} =
-        erl_scan_string("16#eg@", {1,1}, []),
-
     UnderscoreSamples =
         [{"16#1234_ABCD_EF56", 16#1234abcdef56},
          {"2#0011_0101_0011", 2#001101010011},
@@ -376,7 +381,7 @@ base_integers() ->
          fun({S, I}) ->
                  test_string(S, [{integer, {1, 1}, I}])
          end, UnderscoreSamples),
-    UnderscoreErrors =
+    IntegerErrors =
         ["16_#123ABC",
          "16#123_",
          "16#_123",
@@ -384,17 +389,23 @@ base_integers() ->
          "16#_ABC",
          "2#_0101",
          "1__6#ABC",
-         "16#AB__CD"],
+         "16#AB__CD",
+         "16#eg",
+         "16#ef@",
+         "10_#",
+         "10#12a4",
+         "10#12A4"],
     lists:foreach(
       fun(S) ->
               case erl_scan:string(S) of
-                  {ok, [{integer, _, _}|_], _} ->
-                      error({unexpected_integer, S});
-                  _ ->
-                      ok
+                  {error,{1,erl_scan,{illegal,integer}},_} ->
+                      ok;
+                  {error,Err,_} ->
+                      error({unexpected_error, S, Err});
+                  Succ ->
+                      error({unexpected_success, S, Succ})
               end
-      end, UnderscoreErrors),
-    test_string("16#123_", [{integer,{1,1},291},{var,{1,7},'_'}]),
+      end, IntegerErrors),
     test_string("_16#ABC", [{var,{1,1},'_16'},{'#',{1,4}},{var,{1,5},'ABC'}]),
     ok.
 
@@ -405,7 +416,6 @@ floats() ->
          test_string(FS, Ts)
      end || FS <- ["1.0","001.17","3.31200","1.0e0","1.0E17",
                    "34.21E-18", "17.0E+14"]],
-    test_string("1.e2", [{integer,{1,1},1},{'.',{1,2}},{atom,{1,3},e2}]),
 
     {error,{1,erl_scan,{illegal,float}},1} =
         erl_scan:string("1.0e400"),
@@ -430,25 +440,29 @@ floats() ->
          fun({S, I}) ->
                  test_string(S, [{float, {1, 1}, I}])
          end, UnderscoreSamples),
-    UnderscoreErrors =
-        ["123_.456",
-         "123._456",
-         "123.456_",
-         "123._",
-         "1._23e10",
+    FloatErrors =
+        ["123.456_",
+         "1.23_e10",
          "1.23e_10",
-         "1.23e10_"],
+         "1.23e10_",
+         "123.45_e6",
+         "123.45a12",
+         "123.45e23a12",
+         "1.e2",
+         "12._34",
+         "123.a4"
+        ],
     lists:foreach(
       fun(S) ->
               case erl_scan:string(S) of
-                  {ok, [{float, _, _}|_], _} ->
-                      error({unexpected_float, S});
-                  _ ->
-                      ok
+                  {error,{1,erl_scan,{illegal,float}},_} ->
+                      ok;
+                  {error,Err,_} ->
+                      error({unexpected_error, S, Err});
+                  Succ ->
+                      error({unexpected_success, S, Succ})
               end
-      end, UnderscoreErrors),
-    test_string("123._", [{integer,{1,1},123},{'.',{1,4}},{var,{1,5},'_'}]),
-    test_string("1.23_e10", [{float,{1,1},1.23},{var,{1,5},'_e10'}]),
+      end, FloatErrors),
     ok.
 
 dots() ->