diff --git a/extra/modern/modern.factor b/extra/modern/modern.factor
index b7bc19190a..5a45bb03b0 100644
--- a/extra/modern/modern.factor
+++ b/extra/modern/modern.factor
@@ -11,7 +11,6 @@ ERROR: string-expected-got-eof n string ;
 ERROR: long-opening-mismatch tag open n string ch ;
 
 SYMBOL: strict-upper
-
 SYMBOL: delimiter-stack
 : push-delimiter-stack ( obj -- ) delimiter-stack get push ;
 : pop-delimiter-stack ( -- obj ) delimiter-stack get pop ;
@@ -150,8 +149,18 @@ MACRO:: read-matched ( ch -- quot: ( n string tag -- n' string slice' ) )
         merge-slice-til-whitespace
     ] if ;
 
+: terminator? ( slice -- ? )
+    {
+        [ ";" sequence= ]
+    } 1|| ;
+
+ERROR: token-expected n string obj ;
+ERROR: unexpected-terminator n string slice ;
 : read-lowercase-colon ( n string slice -- n' string lowercase-colon )
-    [ lex-factor ] dip swap 2array ;
+    [
+        lex-factor dup [ token-expected ] unless
+        dup terminator? [ unexpected-terminator ] when
+    ] dip swap 2array ;
 
 : strict-upper? ( string -- ? )
     [ { [ CHAR: A CHAR: Z between? ] [ ":-" member? ] } 1|| ] all? ;
diff --git a/extra/modern/slices/slices.factor b/extra/modern/slices/slices.factor
index 6ad44376d3..c0a250d5f1 100644
--- a/extra/modern/slices/slices.factor
+++ b/extra/modern/slices/slices.factor
@@ -95,7 +95,7 @@ ERROR: unexpected-end n string ;
         n string f f
     ] if ; inline
 
-: skip-whitespace ( n string -- n' string )
+: skip-whitespace ( n/f string -- n'/f string )
     slice-til-not-whitespace 2drop ;
 
 : empty-slice-end ( seq -- slice )
@@ -169,7 +169,7 @@ ERROR: unexpected-end n string ;
         [ [ 1 - ] change-to ] dip
     ] when ;
 
-:: slice-til-either ( n string tokens -- n'/f string slice/f ch )
+:: slice-til-either ( n string tokens -- n'/f string slice/f ch/f )
     n [
         n string '[ tokens member? ] find-from
         dup "\s\r\n" member? [