diff --git a/resources/testdata/DoubleComponentError/Bold.ufo/glyphs/contents.plist b/resources/testdata/DoubleComponentError/Bold.ufo/glyphs/contents.plist
new file mode 100644
index 00000000..f6c9c331
--- /dev/null
+++ b/resources/testdata/DoubleComponentError/Bold.ufo/glyphs/contents.plist
@@ -0,0 +1,10 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+  <dict>
+    <key>inner</key>
+    <string>inner.glif</string>
+    <key>outer</key>
+    <string>outer.glif</string>
+  </dict>
+</plist>
diff --git a/resources/testdata/DoubleComponentError/Bold.ufo/glyphs/inner.glif b/resources/testdata/DoubleComponentError/Bold.ufo/glyphs/inner.glif
new file mode 100644
index 00000000..7032a259
--- /dev/null
+++ b/resources/testdata/DoubleComponentError/Bold.ufo/glyphs/inner.glif
@@ -0,0 +1,10 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<glyph name="inner" format="2">
+  <outline>
+    <contour>
+      <point x="10" y="10"/>
+      <point x="30" y="20"/>
+      <point x="10" y="30"/>
+    </contour>
+  </outline>
+</glyph>
diff --git a/resources/testdata/DoubleComponentError/Bold.ufo/glyphs/outer.glif b/resources/testdata/DoubleComponentError/Bold.ufo/glyphs/outer.glif
new file mode 100644
index 00000000..1cb9ce04
--- /dev/null
+++ b/resources/testdata/DoubleComponentError/Bold.ufo/glyphs/outer.glif
@@ -0,0 +1,12 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<glyph name="outer" format="2">
+  <outline>
+    <contour>
+      <point x="30" y="10"/>
+      <point x="50" y="20"/>
+      <point x="30" y="30"/>
+    </contour>
+    <component base="inner" xOffset="100"/>
+    <component base="inner"/>
+  </outline>
+</glyph>
diff --git a/resources/testdata/DoubleComponentError/Bold.ufo/layercontents.plist b/resources/testdata/DoubleComponentError/Bold.ufo/layercontents.plist
new file mode 100644
index 00000000..b9c1a4f2
--- /dev/null
+++ b/resources/testdata/DoubleComponentError/Bold.ufo/layercontents.plist
@@ -0,0 +1,10 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+  <array>
+    <array>
+      <string>public.default</string>
+      <string>glyphs</string>
+    </array>
+  </array>
+</plist>
diff --git a/resources/testdata/DoubleComponentError/Bold.ufo/metainfo.plist b/resources/testdata/DoubleComponentError/Bold.ufo/metainfo.plist
new file mode 100644
index 00000000..7b8b34ac
--- /dev/null
+++ b/resources/testdata/DoubleComponentError/Bold.ufo/metainfo.plist
@@ -0,0 +1,10 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+  <dict>
+    <key>creator</key>
+    <string>com.github.fonttools.ufoLib</string>
+    <key>formatVersion</key>
+    <integer>3</integer>
+  </dict>
+</plist>
diff --git a/resources/testdata/DoubleComponentError/OuterInner.designspace b/resources/testdata/DoubleComponentError/OuterInner.designspace
new file mode 100644
index 00000000..a87a75ed
--- /dev/null
+++ b/resources/testdata/DoubleComponentError/OuterInner.designspace
@@ -0,0 +1,18 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<designspace format="5.0">
+  <axes>
+    <axis tag="wght" name="Weight" minimum="400" maximum="700" default="400"/>
+  </axes>
+  <sources>
+    <source filename="Regular.ufo">
+      <location>
+        <dimension name="Weight" xvalue="400"/>
+      </location>
+    </source>
+    <source filename="Bold.ufo">
+      <location>
+        <dimension name="Weight" xvalue="700"/>
+      </location>
+    </source>
+  </sources>
+</designspace>
diff --git a/resources/testdata/DoubleComponentError/Regular.ufo/glyphs/contents.plist b/resources/testdata/DoubleComponentError/Regular.ufo/glyphs/contents.plist
new file mode 100644
index 00000000..f6c9c331
--- /dev/null
+++ b/resources/testdata/DoubleComponentError/Regular.ufo/glyphs/contents.plist
@@ -0,0 +1,10 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+  <dict>
+    <key>inner</key>
+    <string>inner.glif</string>
+    <key>outer</key>
+    <string>outer.glif</string>
+  </dict>
+</plist>
diff --git a/resources/testdata/DoubleComponentError/Regular.ufo/glyphs/inner.glif b/resources/testdata/DoubleComponentError/Regular.ufo/glyphs/inner.glif
new file mode 100644
index 00000000..7032a259
--- /dev/null
+++ b/resources/testdata/DoubleComponentError/Regular.ufo/glyphs/inner.glif
@@ -0,0 +1,10 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<glyph name="inner" format="2">
+  <outline>
+    <contour>
+      <point x="10" y="10"/>
+      <point x="30" y="20"/>
+      <point x="10" y="30"/>
+    </contour>
+  </outline>
+</glyph>
diff --git a/resources/testdata/DoubleComponentError/Regular.ufo/glyphs/outer.glif b/resources/testdata/DoubleComponentError/Regular.ufo/glyphs/outer.glif
new file mode 100644
index 00000000..27f508a1
--- /dev/null
+++ b/resources/testdata/DoubleComponentError/Regular.ufo/glyphs/outer.glif
@@ -0,0 +1,12 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<glyph name="outer" format="2">
+  <outline>
+    <contour>
+      <point x="30" y="10"/>
+      <point x="50" y="20"/>
+      <point x="30" y="30"/>
+    </contour>
+    <component base="inner"/>
+    <component base="inner"/>
+  </outline>
+</glyph>
diff --git a/resources/testdata/DoubleComponentError/Regular.ufo/layercontents.plist b/resources/testdata/DoubleComponentError/Regular.ufo/layercontents.plist
new file mode 100644
index 00000000..b9c1a4f2
--- /dev/null
+++ b/resources/testdata/DoubleComponentError/Regular.ufo/layercontents.plist
@@ -0,0 +1,10 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+  <array>
+    <array>
+      <string>public.default</string>
+      <string>glyphs</string>
+    </array>
+  </array>
+</plist>
diff --git a/resources/testdata/DoubleComponentError/Regular.ufo/metainfo.plist b/resources/testdata/DoubleComponentError/Regular.ufo/metainfo.plist
new file mode 100644
index 00000000..7b8b34ac
--- /dev/null
+++ b/resources/testdata/DoubleComponentError/Regular.ufo/metainfo.plist
@@ -0,0 +1,10 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+  <dict>
+    <key>creator</key>
+    <string>com.github.fonttools.ufoLib</string>
+    <key>formatVersion</key>
+    <integer>3</integer>
+  </dict>
+</plist>