diff --git a/icu4c/source/common/unicode/unifilt.h b/icu4c/source/common/unicode/unifilt.h
index 9d20a46994..55e7665176 100644
--- a/icu4c/source/common/unicode/unifilt.h
+++ b/icu4c/source/common/unicode/unifilt.h
@@ -89,7 +89,7 @@ public:
      *
      * @draft ICU 2.2
      */
-    virtual inline UClassID getDynamicClassID() const { return getStaticClassID(); }
+    virtual inline UClassID getDynamicClassID() const = 0;
 
     /**
      * ICU "poor man's RTTI", returns a UClassID for this class.
diff --git a/icu4c/source/common/unicode/unifunct.h b/icu4c/source/common/unicode/unifunct.h
index c3fb041bbd..34f088d05e 100644
--- a/icu4c/source/common/unicode/unifunct.h
+++ b/icu4c/source/common/unicode/unifunct.h
@@ -97,7 +97,7 @@ class U_COMMON_API UnicodeFunctor : public UObject {
      * class have the same class ID.  Objects of other classes have
      * different class IDs.
      */
-    virtual UClassID getDynamicClassID(void) const { return getStaticClassID(); }
+    virtual UClassID getDynamicClassID(void) const = 0;
 
     /**
      * Set the data object associated with this functor.  The data