diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+## Changes in 0.21.1
+  - Allow dependency constraints to be numbers (see #234)
+
 ## Changes in 0.21.0
   - Accept section-specific fields in conditionals (see #175, thanks to Scott
     Fleischman)
diff --git a/hpack.cabal b/hpack.cabal
--- a/hpack.cabal
+++ b/hpack.cabal
@@ -1,11 +1,11 @@
--- This file has been generated from package.yaml by hpack version 0.20.0.
+-- This file has been generated from package.yaml by hpack version 0.21.0.
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: db045f3697ddf50f10677f67652465713155419437cab6c893deede5a3330f31
+-- hash: e632b2c7492b7b1a42a6c95bdf1b94a5a800b10cc81d785ee085456a5ef719c1
 
 name:           hpack
-version:        0.21.0
+version:        0.21.1
 synopsis:       An alternative format for Haskell packages
 description:    See README at <https://github.com/sol/hpack#readme>
 category:       Development
@@ -41,6 +41,7 @@
     , directory
     , filepath
     , pretty
+    , scientific
     , text
     , transformers
     , unordered-containers
@@ -83,6 +84,7 @@
     , filepath
     , hpack
     , pretty
+    , scientific
     , text
     , transformers
     , unordered-containers
@@ -117,6 +119,7 @@
     , interpolate
     , mockery >=0.3
     , pretty
+    , scientific
     , temporary
     , text
     , transformers
diff --git a/src/Hpack/Dependency.hs b/src/Hpack/Dependency.hs
--- a/src/Hpack/Dependency.hs
+++ b/src/Hpack/Dependency.hs
@@ -20,6 +20,7 @@
 import qualified Distribution.Version as D
 import           Data.Map.Lazy (Map)
 import qualified Data.Map.Lazy as Map
+import           Data.Scientific
 import           Data.Aeson.Types
 import           Control.Applicative
 import           GHC.Exts
@@ -65,11 +66,21 @@
   parseJSON v = case v of
     Null -> return AnyVersion
     Object _ -> SourceDependency <$> parseJSON v
+    Number n -> return (scientificToDependencyVersion n)
     String s -> parseVersionRange ("== " ++ input) <|> parseVersionRange input
       where
         input = T.unpack s
 
-    _ -> typeMismatch "Null, Object, or String" v
+    _ -> typeMismatch "Null, Object, Number, or String" v
+
+scientificToDependencyVersion :: Scientific -> DependencyVersion
+scientificToDependencyVersion n = VersionRange ("==" ++ version)
+  where
+    version = formatScientific Fixed (Just decimalPlaces) n
+    decimalPlaces
+      | e < 0 = abs e
+      | otherwise = 0
+    e = base10Exponent n
 
 instance FromJSON SourceDependency where
   parseJSON = withObject "SourceDependency" (\o -> let
diff --git a/test/Hpack/DependencySpec.hs b/test/Hpack/DependencySpec.hs
--- a/test/Hpack/DependencySpec.hs
+++ b/test/Hpack/DependencySpec.hs
@@ -109,8 +109,34 @@
 
         it "rejects invalid values" $ do
           [i|
-            hpack: 23
-          |] `parsesAs` Left "Error in $.hpack: expected Null, Object, or String, encountered Number"
+            hpack: []
+          |] `parsesAs` Left "Error in $.hpack: expected Null, Object, Number, or String, encountered Array"
+
+        context "when the constraint is a Number" $ do
+          it "accepts 1" $ do
+            [i|
+              hpack: 1
+            |] `parsesAs` Right [("hpack", VersionRange "==1")]
+
+          it "accepts 1.0" $ do
+            [i|
+              hpack: 1.0
+            |] `parsesAs` Right [("hpack", VersionRange "==1.0")]
+
+          it "accepts 0.11" $ do
+            [i|
+              hpack: 0.11
+            |] `parsesAs` Right [("hpack", VersionRange "==0.11")]
+
+          it "accepts 0.110" $ do
+            [i|
+              hpack: 0.110
+            |] `parsesAs` Right [("hpack", VersionRange "==0.110")]
+
+          it "accepts 1e2" $ do
+            [i|
+              hpack: 1e2
+            |] `parsesAs` Right [("hpack", VersionRange "==100")]
 
         context "when the constraint is a String" $ do
           it "accepts version ranges" $ do