diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Change Log
 
+## 0.7.2 - 2018-03-13
+
+* Add Semigroup instance for MaxVars to build with ghc-8.4
+
 ## 0.7.1 - 2018-02-17
 
 * Export HeapProfBreakdown, HeapProfFlags, and PID types ([#35](https://github.com/haskell/ghc-events/pull/35))
diff --git a/ghc-events.cabal b/ghc-events.cabal
--- a/ghc-events.cabal
+++ b/ghc-events.cabal
@@ -1,5 +1,5 @@
 name:             ghc-events
-version:          0.7.1
+version:          0.7.2
 synopsis:         Library and tool for parsing .eventlog files from GHC
 description:      Parses .eventlog files emitted by GHC 6.12.1 and later.
                   Includes the ghc-events tool permitting, in particular,
@@ -20,8 +20,8 @@
 maintainer:       Simon Marlow <marlowsd@gmail.com>
 bug-reports:      https://github.com/haskell/ghc-events/issues
 build-type:       Simple
-tested-with:      GHC == 7.6.1, GHC == 7.6.3, GHC == 7.8.2, GHC == 7.8.3, GHC == 7.10.1,
-                  GHC == 8.0.2, GHC == 8.2.1
+tested-with:      GHC == 7.8.2, GHC == 7.8.3, GHC == 7.10.1,
+                  GHC == 8.0.2, GHC == 8.2.1, GHC == 8.4.1
 cabal-version:    >= 1.8
 extra-source-files: include/EventLogFormat.h
                     test/queens-ghc-6.12.1.eventlog
@@ -58,7 +58,7 @@
   location: git@github.com:haskell/ghc-events.git
 
 library
-  build-depends:    base       == 4.*,
+  build-depends:    base       >= 4 && < 4.12,
                     containers >= 0.5 && < 0.6,
                     binary     >= 0.7 && < 0.10,
                     bytestring >= 0.10.4,
diff --git a/src/GHC/RTS/Events/Merge.hs b/src/GHC/RTS/Events/Merge.hs
--- a/src/GHC/RTS/Events/Merge.hs
+++ b/src/GHC/RTS/Events/Merge.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 module GHC.RTS.Events.Merge (mergeEventLogs) where
 
 import GHC.RTS.Events
@@ -47,6 +48,11 @@
                        , mcap :: !Int
                        , mthread :: !ThreadId }
 -- TODO introduce parallel RTS process and machine var.s
+
+#if MIN_VERSION_base(4,11,0)
+instance Semigroup MaxVars where
+    (<>) = mappend
+#endif
 
 instance Monoid MaxVars where
     mempty  = MaxVars 0 0 0