diff --git a/core/modern/lexer/lexer.factor b/core/modern/lexer/lexer.factor
index 13ed261bcc..8540536317 100644
--- a/core/modern/lexer/lexer.factor
+++ b/core/modern/lexer/lexer.factor
@@ -14,6 +14,21 @@ CONSTRUCTOR: <modern-lexer> modern-lexer ( string -- obj )
 : ?lexer-nth ( lexer -- obj )
     >lexer< over [ ?nth ] [ 2drop f ] if ;
 
+: lexer-eof? ( lexer -- obj )
+    n>> >boolean ;
+
+: push-tag ( lexer tag -- )
+    swap stack>> push ;
+
+: peek-tag ( lexer -- tag )
+    stack>> ?last ;
+
+: pop-tag ( lexer -- tag )
+    stack>> [ f ] [ pop ] if-empty ;
+
+: roll-back-lexer ( lexer slice -- )
+    from>> >>n drop ;
+
 ERROR: unexpected-end n string ;
 : nth-check-eof ( n string -- nth )
     2dup ?nth [ 2nip ] [ unexpected-end ] if* ; inline
diff --git a/core/modern/modern.factor b/core/modern/modern.factor
index dcd1a7d8b8..eda8dec7f8 100644
--- a/core/modern/modern.factor
+++ b/core/modern/modern.factor
@@ -126,7 +126,7 @@ M: array collapse-decorators
 : scoped-less-than-name ( string -- string' )
     dup [ length 2 - ] keep [ char: < = ] find-last-from [ 1 + tail ] [ drop ] if ;
 
-: scoped-upper? ( string -- ? )
+: top-level-name? ( string -- ? )
     dup { [ ":" tail? ] [ "<" tail? ] } 1|| [
         dup length 1 > [
             [ [ ":<" member? ] trim-tail [ char: \: = ] find-last ] keep
@@ -138,6 +138,18 @@ M: array collapse-decorators
         drop f
     ] if ;
 
+: top-level-colon? ( string -- ? )
+    dup ":" tail? [
+        dup length 1 > [
+            [ [ char: \: = ] trim-tail [ char: \: = ] find-last ] keep
+            swap [ swap tail strict-upper? ] [ nip strict-upper? ] if
+        ] [
+            ":" sequence=
+        ] if
+    ] [
+        drop f
+    ] if ;
+
 ERROR: whitespace-expected-after n string ch ;
 ERROR: expected-more-tokens n string expected ;
 ERROR: string-expected-got-eof n string ;
@@ -249,17 +261,17 @@ ERROR: unnestable-form n string obj ;
 ! For implementing [ { (
 : lex-until ( lexer tags -- payload closing )
     ! over lexer-found-eof? [ "more tokens expected" throw ] when
-    2dup '[
+    '[
         [
-            _ B lex-factor [
+            _ lex-factor [
                 dup tag-literal? [
                     dup ,
-                    underlying>> ! { [ dup scoped-upper? ] [ 4 npick 0 > ] } 0&& [ unnestable-form ] when
+                    underlying>> ! { [ dup top-level-name? ] [ 4 npick 0 > ] } 0&& [ unnestable-form ] when
                     _ [ sequence= ] with any? not
                 ] [ , t ] if
             ] [
-                _ _ lex-expected-but-got-eof
                 f , f
+                ! _ _ over lexer-eof? [ lex-expected-but-got-eof ] [ 2drop f , f ] if
             ] if*
         ] loop
     ] { } make unclip-last ; inline
@@ -311,11 +323,18 @@ MACRO:: read-matched ( ch -- quot: ( lexer tag -- slice' ) )
 
 
 ERROR: cannot-nest-upper-colon n string string' ;
-: read-upper-colon ( lexer string' -- obj )
+: read-upper-colon ( lexer string' -- obj/f )
     ! 4 npick 0 > [ cannot-nest-upper-colon ] when
-    dup [
-        [ but-last ";" append ";" 2array ] [ ";" 1array ] if* lex-until
-    ] dip 1 cut-slice* uppercase-colon-literal make-matched-literal ;
+    over peek-tag top-level-colon? [
+        ! roll back, nested upper
+        roll-back-lexer f
+    ] [
+        2dup push-tag [
+            dup [
+                [ but-last ";" append ";" 2array ] [ ";" 1array ] if* lex-until
+            ] dip 1 cut-slice* uppercase-colon-literal make-matched-literal
+        ] 2keep drop pop-tag drop
+    ] if ;
 
 : read-lower-colon ( lexer string' -- obj )
     [ lex-factor dup ] dip 1 cut-slice*
@@ -327,7 +346,7 @@ ERROR: cannot-nest-upper-colon n string string' ;
         { [ dup length 1 = ] [ read-upper-colon ] }
         { [ dup [ char: \: = ] all? ] [ read-upper-colon ] }
         { [ dup { [ ":" head? ] [ ":" tail? ] } 1&& ] [ nip make-tag-literal ] }
-        { [ dup ":" tail? ] [ dup scoped-upper? [ read-upper-colon ] [ read-lower-colon ] if ] }
+        { [ dup ":" tail? ] [ dup top-level-name? [ read-upper-colon ] [ read-lower-colon ] if ] }
         { [ dup ":" head? ] [ nip make-tag-literal ] } ! :foo( ... )
         [ nip make-tag-literal ]
     } cond ;
@@ -341,7 +360,7 @@ ERROR: cannot-nest-upper-colon n string string' ;
 : read-less-than ( lexer slice -- less-than )
     dupd merge-lex-til-whitespace {
         { [ dup length 1 = ] [ nip make-tag-literal ] } ! "<"
-        { [ dup "<" tail? ] [ dup scoped-upper? [ read-upper-less-than ] [ nip make-tag-literal ] if ] } ! FOO< or foo<
+        { [ dup "<" tail? ] [ dup top-level-name? [ read-upper-less-than ] [ nip make-tag-literal ] if ] } ! FOO< or foo<
         [ nip make-tag-literal ]
     } cond ;