diff --git a/packages/core/src/components/forms/_file-upload.scss b/packages/core/src/components/forms/_file-upload.scss
index 96135e9572..a96ea1ad68 100644
--- a/packages/core/src/components/forms/_file-upload.scss
+++ b/packages/core/src/components/forms/_file-upload.scss
@@ -19,18 +19,21 @@ Wrap that all in a `label` with class `pt-file-upload`.
 </div>
 
 Markup:
-<label class="pt-file-upload">
+<label class="pt-file-upload {{.modifier}}">
   <input type="file" {{:modifier}}/>
   <span class="pt-file-upload-input">Choose file...</span>
 </label>
 
 :disabled - Disabled
+.pt-fill - Take up full width of parent element
 
 Weight: 10
 
 Styleguide components.forms.fileupload
 */
 
+$file-upload-button-width: $pt-grid-size * 7;
+
 .pt-file-upload {
   display: inline-block;
   position: relative;
@@ -70,7 +73,7 @@ Styleguide components.forms.fileupload
     top: 0;
     right: 0;
     left: 0;
-    margin-right: $pt-grid-size * 7;
+    margin-right: $file-upload-button-width;
     border-top-right-radius: 0;
     border-bottom-right-radius: 0;
     height: $pt-input-height;
@@ -88,7 +91,8 @@ Styleguide components.forms.fileupload
       border-radius: $pt-border-radius;
       border-top-left-radius: 0;
       border-bottom-left-radius: 0;
-      width: $pt-grid-size * 7;
+      // compensating for the negative margin-left above
+      width: $file-upload-button-width + $button-border-width;
       height: $pt-input-height;
       padding: 0 $pt-grid-size;
       text-align: center;
@@ -121,4 +125,8 @@ Styleguide components.forms.fileupload
       }
     }
   }
+
+  &.pt-fill {
+    width: 100%;
+  }
 }