diff --git a/packages/gatsby-plugin-sharp/src/index.js b/packages/gatsby-plugin-sharp/src/index.js
index 8237bc0abe00d..0b3d080cd568f 100644
--- a/packages/gatsby-plugin-sharp/src/index.js
+++ b/packages/gatsby-plugin-sharp/src/index.js
@@ -127,13 +127,14 @@ const processFile = (file, jobs, cb, reporter) => {
     } else {
       clonedPipeline = pipeline
     }
-    // Sharp only allows ints as height/width. Since height isn't always
-    // set, check first before trying to round it.
-    let roundedHeight = args.height
-    if (roundedHeight) {
-      roundedHeight = Math.round(roundedHeight)
-    }
-    const roundedWidth = Math.round(args.width)
+    // Sharp only allows ints as height/width. Since either height or width
+    // could not be set, check first before trying to round them.
+    let roundedHeight = args.hasOwnProperty(args, `height`)
+      ? Math.round(args.height)
+      : undefined
+    const roundedWidth = args.hasOwnProperty(args, `width`)
+      ? Math.round(args.width)
+      : undefined
     clonedPipeline
       .resize(roundedWidth, roundedHeight)
       .crop(args.cropFocus)
diff --git a/packages/gatsby-transformer-sharp/src/extend-node-type.js b/packages/gatsby-transformer-sharp/src/extend-node-type.js
index f8a8159b9ac0f..f8d2af200a89c 100644
--- a/packages/gatsby-transformer-sharp/src/extend-node-type.js
+++ b/packages/gatsby-transformer-sharp/src/extend-node-type.js
@@ -105,7 +105,6 @@ const fixedNodeType = ({
     args: {
       width: {
         type: GraphQLInt,
-        defaultValue: 400,
       },
       height: {
         type: GraphQLInt,
@@ -222,7 +221,6 @@ const fluidNodeType = ({
     args: {
       maxWidth: {
         type: GraphQLInt,
-        defaultValue: 800,
       },
       maxHeight: {
         type: GraphQLInt,