diff --git a/CHANGES.markdown b/CHANGES.markdown
--- a/CHANGES.markdown
+++ b/CHANGES.markdown
@@ -1,3 +1,8 @@
+0.6.0.2: 5 March 2013
+---------------------
+
+* bug fix: the 'diameter' and 'radius' functions now work correctly.
+
 0.6.0.1: 7 January 2013
 -----------------------
 
diff --git a/diagrams-core.cabal b/diagrams-core.cabal
--- a/diagrams-core.cabal
+++ b/diagrams-core.cabal
@@ -1,5 +1,5 @@
 Name:                diagrams-core
-Version:             0.6.0.1
+Version:             0.6.0.2
 Synopsis:            Core libraries for diagrams EDSL
 Description:         The core modules underlying diagrams,
                      an embedded domain-specific language
diff --git a/src/Diagrams/Core/Envelope.hs b/src/Diagrams/Core/Envelope.hs
--- a/src/Diagrams/Core/Envelope.hs
+++ b/src/Diagrams/Core/Envelope.hs
@@ -251,7 +251,7 @@
 --   vector.  Returns zero for the empty envelope.
 diameter :: Enveloped a => V a -> a -> Scalar (V a)
 diameter v a = case appEnvelope $ getEnvelope a of
-  (Just env) -> (env v - env (negateV v)) * magnitude v
+  (Just env) -> (env v + env (negateV v)) * magnitude v
   Nothing -> 0
 
 -- | Compute the \"radius\" (1\/2 the diameter) of an enveloped object