diff --git a/basis/compression/lzw/lzw.factor b/basis/compression/lzw/lzw.factor
index f61a02c01b..248700b08c 100755
--- a/basis/compression/lzw/lzw.factor
+++ b/basis/compression/lzw/lzw.factor
@@ -1,7 +1,7 @@
 ! Copyright (C) 2009 Doug Coleman.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: accessors combinators io kernel math namespaces
-sequences vectors ;
+USING: accessors combinators io kernel math math.order
+namespaces sequences vectors ;
 QUALIFIED-WITH: bitstreams bs
 IN: compression.lzw
 
@@ -62,8 +62,13 @@ GENERIC: code-space-full? ( lzw -- ? )
 M: tiff-lzw code-space-full? size-and-limit 1 - = ;
 M: gif-lzw code-space-full? size-and-limit = ;
 
+GENERIC: increment-code-size ( lzw -- lzw )
+
+M: lzw increment-code-size [ 1 + ] change-code-size ;
+M: gif-lzw increment-code-size [ 1 + 12 min ] change-code-size ;
+
 : maybe-increment-code-size ( lzw -- lzw )
-    dup code-space-full? [ [ 1 + ] change-code-size ] when ;
+    dup code-space-full? [ increment-code-size ] when ;
 
 : add-to-table ( seq lzw -- )
     [ table>> push ]
@@ -108,7 +113,7 @@ DEFER: lzw-uncompress-char
             [ output>> push-all ] [ add-to-table ] 2bi
         ] [ code>old-code ] bi
     ] if ;
-    
+
 : lzw-uncompress-char ( lzw -- )
     [ >>code handle-uncompress-code lzw-uncompress-char ]
     lzw-process-next-code ;
diff --git a/basis/images/loader/loader.factor b/basis/images/loader/loader.factor
index 7e1dc9ca31..52a80459d9 100644
--- a/basis/images/loader/loader.factor
+++ b/basis/images/loader/loader.factor
@@ -13,9 +13,11 @@ ERROR: unknown-image-extension extension ;
 SYMBOL: types
 types [ H{ } clone ] initialize
 
+: (image-class) ( type -- class )
+    >lower types get ?at [ unknown-image-extension ] unless ;
+
 : image-class ( path -- class )
-    file-extension >lower types get ?at
-    [ unknown-image-extension ] unless ;
+    file-extension (image-class) ;
 
 : open-image-file ( path -- stream )
     binary <limited-file-reader> ;
diff --git a/core/sets/sets.factor b/core/sets/sets.factor
index 06f6e04655..5dcee675f9 100644
--- a/core/sets/sets.factor
+++ b/core/sets/sets.factor
@@ -109,7 +109,7 @@ M: sequence null?
 M: sequence cardinality
     length ;
 
-: combine ( sets -- set )
+: combine ( sets -- set/f )
     [ f ]
     [ [ [ members ] map concat ] [ first ] bi set-like ]
     if-empty ;
diff --git a/extra/images/gif/gif.factor b/extra/images/gif/gif.factor
index b06210fc00..8d4b118d16 100644
--- a/extra/images/gif/gif.factor
+++ b/extra/images/gif/gif.factor
@@ -140,7 +140,8 @@ ERROR: unimplemented message ;
 : sort? ( image -- ? ) flags>> 5 bit? ; inline
 : color-table-size ( image -- ? ) flags>> 3 bits 1 + 2^ 3 * ; inline
 : transparency? ( image -- ? )
-    graphic-control-extensions>> first flags>> 0 bit? ; inline
+    graphic-control-extensions>>
+    [ f ] [ first flags>> 0 bit? ] if-empty ; inline
 
 : color-resolution ( image -- ? ) flags>> -4 shift 3 bits ; inline
 
diff --git a/extra/images/http/http.factor b/extra/images/http/http.factor
index 620ab6f73b..217c8408d1 100644
--- a/extra/images/http/http.factor
+++ b/extra/images/http/http.factor
@@ -1,11 +1,21 @@
 ! Copyright (C) 2009 Doug Coleman.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: http.client images.loader images.loader.private kernel
-images.viewer ;
+USING: accessors assocs http.client images.loader
+images.loader.private images.viewer io.pathnames kernel
+namespaces sequences ;
 IN: images.http
 
+<PRIVATE
+
+: content-type ( response -- type/f )
+    content-type>> dup "image/" head?
+    [ 6 tail ] [ drop f ] if ;
+
+PRIVATE>
+
 : load-http-image ( path -- image )
-    [ http-get nip ] [ image-class ] bi load-image* ;
+    [ http-get swap content-type ] [ file-extension ] bi or
+    (image-class) load-image* ;
 
 : http-image. ( path -- )
     load-http-image image. ;