diff --git a/mailnews/import/src/nsImportService.cpp b/mailnews/import/src/nsImportService.cpp
index a39e8ed3ecab..3020be7bd863 100644
--- a/mailnews/import/src/nsImportService.cpp
+++ b/mailnews/import/src/nsImportService.cpp
@@ -357,6 +357,8 @@ NS_IMETHODIMP nsImportService::SystemStringFromUnicode(const PRUnichar *uniStr,
 
 			// get an unicode converter
 			rv = ccm2->GetUnicodeEncoder(charsetAtom, &m_pEncoder);
+      if (NS_SUCCEEDED(rv))
+        rv = m_pEncoder->SetOutputErrorBehavior(nsIUnicodeEncoder::kOnError_Replace, nsnull, '?');
 		}
 	}