diff --git a/OpenEXR/IlmImf/ImfEnvmapAttribute.h b/OpenEXR/IlmImf/ImfEnvmapAttribute.h
index 0d0129b80a..5036eca228 100644
--- a/OpenEXR/IlmImf/ImfEnvmapAttribute.h
+++ b/OpenEXR/IlmImf/ImfEnvmapAttribute.h
@@ -61,7 +61,9 @@ template <> IMF_EXPORT
 void EnvmapAttribute::readValueFrom (OPENEXR_IMF_INTERNAL_NAMESPACE::IStream &,
                                      int,
                                      int);
-
+template <> IMF_EXPORT
+void
+EnvmapAttribute::copyValueFrom (const OPENEXR_IMF_INTERNAL_NAMESPACE::Attribute &other);
 
 OPENEXR_IMF_INTERNAL_NAMESPACE_HEADER_EXIT