diff --git a/mail-client/thunderbird/thunderbird-78.3.1.ebuild b/mail-client/thunderbird/thunderbird-78.3.1.ebuild
index 70e6b9b482583..70f4e3a221992 100644
--- a/mail-client/thunderbird/thunderbird-78.3.1.ebuild
+++ b/mail-client/thunderbird/thunderbird-78.3.1.ebuild
@@ -412,6 +412,9 @@ pkg_setup() {
 		if [[ -z "${MOZ_API_KEY_GOOGLE+set}" ]] ; then
 			MOZ_API_KEY_GOOGLE="AIzaSyDEAOvatFogGaPi0eTgsV_ZlEzx0ObmepsMzfAc"
 		fi
+
+		# Ensure we use C locale when building, bug #746215
+		export LC_ALL=C
 	fi
 }