diff --git a/src/format/mod.rs b/src/format/mod.rs
index 360c3c5..efd6f76 100644
--- a/src/format/mod.rs
+++ b/src/format/mod.rs
@@ -101,11 +101,25 @@ pub enum Numeric {
 }
 
 /// An opaque type representing numeric item types for internal uses only.
-#[derive(Clone, PartialEq, Eq)]
 pub struct InternalNumeric {
     _dummy: Void,
 }
 
+impl Clone for InternalNumeric {
+    fn clone(&self) -> Self {
+        match self._dummy {}
+    }
+}
+
+impl PartialEq for InternalNumeric {
+    fn eq(&self, _other: &InternalNumeric) -> bool {
+        match self._dummy {}
+    }
+}
+
+impl Eq for InternalNumeric {
+}
+
 impl fmt::Debug for InternalNumeric {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "<InternalNumeric>")
@@ -188,11 +202,25 @@ pub enum Fixed {
 }
 
 /// An opaque type representing fixed-format item types for internal uses only.
-#[derive(Clone, PartialEq, Eq)]
 pub struct InternalFixed {
     _dummy: Void,
 }
 
+impl Clone for InternalFixed {
+    fn clone(&self) -> Self {
+        match self._dummy {}
+    }
+}
+
+impl PartialEq for InternalFixed {
+    fn eq(&self, _other: &InternalFixed) -> bool {
+        match self._dummy {}
+    }
+}
+
+impl Eq for InternalFixed {
+}
+
 impl fmt::Debug for InternalFixed {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "<InternalFixed>")