diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+## 0.6.7006.1
+
+* Add `sumInt4` and `sumInt8` `Aggregator`s, which don't crash at run
+  time (`sum` currently does on those types).
+
+* Add inferrable `FromFields` instance for `SqlNumeric` to
+  `Scientific`.
+
 ## 0.6.7006.0
 
 * Added `Opaleye.RunSelect.runSelectI` and
diff --git a/opaleye.cabal b/opaleye.cabal
--- a/opaleye.cabal
+++ b/opaleye.cabal
@@ -1,6 +1,6 @@
 name:            opaleye
 copyright:       Copyright (c) 2014-2018 Purely Agile Limited; 2019-2020 Tom Ellis
-version:         0.6.7006.0
+version:         0.6.7006.1
 synopsis:        An SQL-generating DSL targeting PostgreSQL
 description:     An SQL-generating DSL targeting PostgreSQL.  Allows
                  Postgres queries to be written within Haskell in a
diff --git a/src/Opaleye/Aggregate.hs b/src/Opaleye/Aggregate.hs
--- a/src/Opaleye/Aggregate.hs
+++ b/src/Opaleye/Aggregate.hs
@@ -99,8 +99,18 @@
 groupBy = A.makeAggr' Nothing
 
 -- | Sum all rows in a group.
+--
+-- WARNING! The type of this operation is wrong and will crash at
+-- runtime when the argument is 'T.SqlInt4' or 'T.SqlInt8'.  For those
+-- use 'sumInt4' or 'sumInt8' instead.
 sum :: Aggregator (C.Column a) (C.Column a)
 sum = A.makeAggr HPQ.AggrSum
+
+sumInt4 :: Aggregator (C.Column T.SqlInt4) (C.Column T.SqlInt8)
+sumInt4 = fmap C.unsafeCoerceColumn Opaleye.Aggregate.sum
+
+sumInt8 :: Aggregator (C.Column T.SqlInt8) (C.Column T.SqlNumeric)
+sumInt8 = fmap C.unsafeCoerceColumn Opaleye.Aggregate.sum
 
 -- | Count the number of non-null rows in a group.
 count :: Aggregator (C.Column a) (C.Column T.SqlInt8)
diff --git a/src/Opaleye/Internal/Inferrable.hs b/src/Opaleye/Internal/Inferrable.hs
--- a/src/Opaleye/Internal/Inferrable.hs
+++ b/src/Opaleye/Internal/Inferrable.hs
@@ -60,6 +60,10 @@
 instance double ~ Double => D.Default (Inferrable FromField) T.SqlFloat8 double where
   def = Inferrable D.def
 
+instance scientific ~ Sci.Scientific
+  => D.Default (Inferrable FromField) T.SqlNumeric scientific where
+  def = Inferrable D.def
+
 instance bool ~ Bool => D.Default (Inferrable FromField) T.SqlBool bool where
   def = Inferrable D.def