diff --git a/gtk/gtkroundedbox.c b/gtk/gtkroundedbox.c
index c3e2650e4c..c89a1fd354 100644
--- a/gtk/gtkroundedbox.c
+++ b/gtk/gtkroundedbox.c
@@ -149,8 +149,10 @@ gtk_css_border_radius_grow (GtkRoundedBoxCorner *corner,
                             double               horizontal,
                             double               vertical)
 {
-  corner->horizontal += horizontal;
-  corner->vertical += vertical;
+  if (corner->horizontal)
+    corner->horizontal += horizontal;
+  if (corner->vertical)
+    corner->vertical += vertical;
 
   if (corner->horizontal <= 0 || corner->vertical <= 0)
     {
diff --git a/testsuite/reftests/Makefile.am b/testsuite/reftests/Makefile.am
index 0b39b41dfd..103b523fde 100644
--- a/testsuite/reftests/Makefile.am
+++ b/testsuite/reftests/Makefile.am
@@ -143,6 +143,9 @@ testdata = \
 	box-shadow-spec-inset.css \
 	box-shadow-spec-inset.ref.ui \
 	box-shadow-spec-inset.ui \
+	box-shadow-spread.css \
+	box-shadow-spread.ref.ui \
+	box-shadow-spread.ui \
 	button-wrapping.ui \
 	button-wrapping.ref.ui \
 	cellrenderer-pixbuf-stock-rtl.css \
diff --git a/testsuite/reftests/box-shadow-spread.css b/testsuite/reftests/box-shadow-spread.css
new file mode 100644
index 0000000000..b22bad4ee5
--- /dev/null
+++ b/testsuite/reftests/box-shadow-spread.css
@@ -0,0 +1,9 @@
+@import "reset-to-defaults.css";
+
+.test {
+  box-shadow: 0 0 0 10px red;
+}
+
+.reference {
+  border: solid 10px red;
+}
diff --git a/testsuite/reftests/box-shadow-spread.ref.ui b/testsuite/reftests/box-shadow-spread.ref.ui
new file mode 100644
index 0000000000..f6894c2b34
--- /dev/null
+++ b/testsuite/reftests/box-shadow-spread.ref.ui
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- Generated with glade 3.18.1 -->
+<interface>
+  <requires lib="gtk+" version="3.12"/>
+  <object class="GtkWindow" id="window1">
+    <property name="width_request">100</property>
+    <property name="height_request">100</property>
+    <property name="can_focus">False</property>
+    <property name="type">popup</property>
+    <child>
+      <object class="GtkButton" id="button1">
+        <property name="label" translatable="yes">Hi</property>
+        <property name="visible">True</property>
+        <property name="can_focus">False</property>
+        <property name="receives_default">False</property>
+        <property name="halign">center</property>
+        <property name="valign">center</property>
+        <style>
+          <class name="reference"/>
+        </style>
+      </object>
+    </child>
+  </object>
+</interface>
diff --git a/testsuite/reftests/box-shadow-spread.ui b/testsuite/reftests/box-shadow-spread.ui
new file mode 100644
index 0000000000..ef4cdea031
--- /dev/null
+++ b/testsuite/reftests/box-shadow-spread.ui
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- Generated with glade 3.18.1 -->
+<interface>
+  <requires lib="gtk+" version="3.12"/>
+  <object class="GtkWindow" id="window1">
+    <property name="width_request">100</property>
+    <property name="height_request">100</property>
+    <property name="can_focus">False</property>
+    <property name="type">popup</property>
+    <child>
+      <object class="GtkButton" id="button1">
+        <property name="label" translatable="yes">Hi</property>
+        <property name="visible">True</property>
+        <property name="can_focus">False</property>
+        <property name="receives_default">False</property>
+        <property name="halign">center</property>
+        <property name="valign">center</property>
+        <style>
+          <class name="test"/>
+        </style>
+      </object>
+    </child>
+  </object>
+</interface>