diff --git a/lib/mergetool.tcl b/lib/mergetool.tcl
index 249e0cf..3c8e73b 100644
--- a/lib/mergetool.tcl
+++ b/lib/mergetool.tcl
@@ -187,6 +187,13 @@
 				 "$LOCAL" "$REMOTE" "$MERGED"]
 		}
 	}
+	bc3 {
+		if {$base_stage ne {}} {
+			set cmdline [list "$merge_tool_path" "$LOCAL" "$REMOTE" "$BASE" -mergeoutput="$MERGED"]
+		} else {
+			set cmdline [list "$merge_tool_path" "$LOCAL" "$REMOTE" -mergeoutput="$MERGED"]
+		}
+	}
 	ecmerge {
 		if {$base_stage ne {}} {
 			set cmdline [list "$merge_tool_path" "$BASE" "$LOCAL" "$REMOTE" --default --mode=merge3 --to="$MERGED"]