diff --git a/res/res_fax.c b/res/res_fax.c
index 604d139066..2ec7d2e3a2 100644
--- a/res/res_fax.c
+++ b/res/res_fax.c
@@ -1663,6 +1663,8 @@ static int receivefax_exec(struct ast_channel *chan, const char *data)
 			ao2_ref(details, -1);
 			return -1;
 		}
+	} else {
+		details->caps |= AST_FAX_TECH_AUDIO;
 	}
 
 	if (!ast_test_flag(&opts, OPT_FORCE_AUDIO) && (details->caps & AST_FAX_TECH_T38)) {
@@ -2145,6 +2147,8 @@ static int sendfax_exec(struct ast_channel *chan, const char *data)
 			ao2_ref(details, -1);
 			return -1;
 		}
+	} else {
+		details->caps |= AST_FAX_TECH_AUDIO;
 	}
 
 	if (!ast_test_flag(&opts, OPT_FORCE_AUDIO) && (details->caps & AST_FAX_TECH_T38)) {