diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,9 +1,15 @@
+# 0.5.4.1
+
+## Bug fixes
+
+ * Fixed an issue where inexact numeric literals (e.g. Haskell type `Double`) were implicitly converted to Postgres `NUMERIC`, triggering a runtime conversion error (#700).
+
 # 0.5.4.0
 
 ## Added features
 
  * Better error messages on column type mismatches (#696).
- * Added support for creating and dropping database schemas and associated tables with `createDatabaseSchema`, `dropDatabaseSchema`, `` and `createTableWithSchema` (#716).
+ * Added support for creating and dropping database schemas and associated tables with `createDatabaseSchema`, `dropDatabaseSchema`, and `createTableWithSchema` (#716).
 
 ## Documentation
  
diff --git a/Database/Beam/Postgres/Syntax.hs b/Database/Beam/Postgres/Syntax.hs
--- a/Database/Beam/Postgres/Syntax.hs
+++ b/Database/Beam/Postgres/Syntax.hs
@@ -100,7 +100,7 @@
 import           Data.Aeson (Value, object, (.=))
 import           Data.Bits
 import           Data.ByteString (ByteString)
-import           Data.ByteString.Builder (Builder, byteString, char8, toLazyByteString)
+import           Data.ByteString.Builder (Builder, doubleDec, floatDec, byteString, char8, toLazyByteString)
 import qualified Data.ByteString.Char8 as B
 import           Data.ByteString.Lazy.Char8 (toStrict)
 import qualified Data.ByteString.Lazy.Char8 as BL
@@ -1202,8 +1202,6 @@
              sqlValueSyntax = defaultPgValueSyntax
 
 DEFAULT_SQL_SYNTAX(Bool)
-DEFAULT_SQL_SYNTAX(Double)
-DEFAULT_SQL_SYNTAX(Float)
 DEFAULT_SQL_SYNTAX(Int8)
 DEFAULT_SQL_SYNTAX(Int16)
 DEFAULT_SQL_SYNTAX(Int32)
@@ -1230,6 +1228,21 @@
 DEFAULT_SQL_SYNTAX(Pg.LocalTimestamp)
 DEFAULT_SQL_SYNTAX(Pg.UTCTimestamp)
 DEFAULT_SQL_SYNTAX(Scientific)
+
+-- We have a 'manual' instance for Double and Float because the default value of a
+-- literal like "1.0" is NUMERIC, not DOUBLE. However, NUMERIC values are exact, 
+-- while DOUBLEs are inexact. This means that converting from SQL NUMERIC
+-- to Haskell Double is lossy.
+-- See #700
+instance HasSqlValueSyntax PgValueSyntax Float where
+  sqlValueSyntax v 
+    | isNaN v || isInfinite v = PgValueSyntax $ emit "'" <> emitBuilder (floatDec v) <> emit "'"
+    | otherwise               = PgValueSyntax $ emit "'" <> emitBuilder (floatDec v) <> emit "'::double precision"
+
+instance HasSqlValueSyntax PgValueSyntax Double where
+  sqlValueSyntax v 
+    | isNaN v || isInfinite v = PgValueSyntax $ emit "'" <> emitBuilder (doubleDec v) <> emit "'"
+    | otherwise               = PgValueSyntax $ emit "'" <> emitBuilder (doubleDec v) <> emit "'::double precision"
 
 instance HasSqlValueSyntax PgValueSyntax (CI T.Text) where
   sqlValueSyntax = sqlValueSyntax . CI.original
diff --git a/beam-postgres.cabal b/beam-postgres.cabal
--- a/beam-postgres.cabal
+++ b/beam-postgres.cabal
@@ -1,5 +1,5 @@
 name:                 beam-postgres
-version:              0.5.4.0
+version:              0.5.4.1
 synopsis:             Connection layer between beam and postgres
 description:          Beam driver for <https://www.postgresql.org/ PostgreSQL>, an advanced open-source RDBMS
 homepage:             https://haskell-beam.github.io/beam/user-guide/backends/beam-postgres
diff --git a/test/Database/Beam/Postgres/Test/DataTypes.hs b/test/Database/Beam/Postgres/Test/DataTypes.hs
--- a/test/Database/Beam/Postgres/Test/DataTypes.hs
+++ b/test/Database/Beam/Postgres/Test/DataTypes.hs
@@ -21,7 +21,8 @@
 tests postgresConn =
     testGroup "Data-type unit tests"
     [ jsonNulTest postgresConn
-    , errorOnSchemaMismatch postgresConn ]
+    , errorOnSchemaMismatch postgresConn
+    , errorOnLiteralDoubles postgresConn ]
 
 data JsonT f
     = JsonT
@@ -136,3 +137,20 @@
 
       assertBool "runInsertReturningList succeeded" didFail
       didFail @?= True
+
+-- | Regression test for <https://github.com/haskell-beam/beam/issues/700>
+errorOnLiteralDoubles :: IO ByteString -> TestTree
+errorOnLiteralDoubles pgConn =
+    testCase "Literal `Double`s are correctly specified as SQL `DOUBLE` (#700)" $ 
+    withTestPostgres "db_failures" pgConn $ \conn -> do
+      results <- runBeamPostgres conn $ 
+        runSelectReturningList $ 
+          select $ 
+            query
+      
+      results @?= [(99 :: Int32, 1.0 :: Double)]
+    
+    where
+      -- We need to provide a db for type-checking, but it will not be used
+      query :: Q Postgres RealDb s (QExpr Postgres s Int32, QExpr Postgres s Double)
+      query = pure (val_ 99, val_ 1.0)