diff --git a/basis/compiler/cfg/builder/blocks/blocks-docs.factor b/basis/compiler/cfg/builder/blocks/blocks-docs.factor
index 7c7b2d6448..d096f7b85f 100644
--- a/basis/compiler/cfg/builder/blocks/blocks-docs.factor
+++ b/basis/compiler/cfg/builder/blocks/blocks-docs.factor
@@ -53,7 +53,7 @@ HELP: emit-conditional
 { $values
   { "block" basic-block }
   { "branches" "sequence of pairs" }
-  { "block'" basic-block }
+  { "block'/f" { $maybe basic-block } }
 }
 { $description "Emits a sequence of conditional branches to the current " { $link cfg } ". Each branch is a pair where the first item is the entry basic block and the second the branches " { $link height-state } ". 'block' is the block in which the control flow is branched and \"block'\" the block in which it converges again." } ;
 
diff --git a/basis/compiler/cfg/builder/blocks/blocks.factor b/basis/compiler/cfg/builder/blocks/blocks.factor
index 12b589e5c0..e3d3006ba5 100644
--- a/basis/compiler/cfg/builder/blocks/blocks.factor
+++ b/basis/compiler/cfg/builder/blocks/blocks.factor
@@ -3,12 +3,10 @@
 USING: accessors arrays compiler.cfg compiler.cfg.instructions
 compiler.cfg.stacks compiler.cfg.stacks.local compiler.cfg.utilities
 kernel make math namespaces sequences ;
-SLOT: in-d
-SLOT: out-d
 IN: compiler.cfg.builder.blocks
 
 : set-basic-block ( basic-block -- )
-    [ instructions>> building set ] [ begin-local-analysis ] bi ;
+    dup begin-local-analysis instructions>> building set ;
 
 : end-basic-block ( block -- )
     [ end-local-analysis ] when* building off ;
@@ -17,7 +15,7 @@ IN: compiler.cfg.builder.blocks
     <basic-block> swap [ over connect-bbs ] when* dup set-basic-block ;
 
 : begin-basic-block ( block -- block' )
-    dup [ end-local-analysis ] when* (begin-basic-block) ;
+    dup end-basic-block (begin-basic-block) ;
 
 : emit-trivial-block ( block quot: ( ..a block' -- ..b ) -- block' )
     ##branch, swap begin-basic-block
@@ -52,7 +50,7 @@ IN: compiler.cfg.builder.blocks
 : with-branch ( block quot: ( ..a block -- ..b block' ) -- pair/f )
     [ [ begin-branch ] dip call end-branch ] with-scope ; inline
 
-: emit-conditional ( block branches -- block' )
+: emit-conditional ( block branches -- block'/f )
     swap end-basic-block
     sift [ f ] [
         dup first second height-state set