diff --git a/Mmakefile b/Mmakefile
index ec39748a0..bf9a5b3b1 100644
--- a/Mmakefile
+++ b/Mmakefile
@@ -437,9 +437,11 @@ install_grades: scripts
 		( cd boehm_gc && rm -f *.$O *.pic_o *.$A *.so ) && \
 		( cd runtime && rm -f *.$O *.pic_o *.$A *.so ) && \
 		( cd library && rm -f *.dep *.h *.c *.c_date *.$O *.pic_o \
-				*.$A *.so Mercury/cs/*.c Mercury/os/*.$O ) && \
+				*.$A *.so Mercury/cs/*.c \
+				Mercury/c_dates/*.c_date Mercury/os/*.$O ) && \
 		( cd browser && rm -f *.dep *.h *.c *.c_date *.$O *.pic_o \
-				*.$A *.so Mercury/cs/*.c Mercury/os/*.$O ) && \
+				*.$A *.so Mercury/cs/*.c \
+				Mercury/c_dates/*.c_date Mercury/os/*.$O ) && \
 		( cd trace && rm -f *.$O *.pic_o *.$A *.so ) && \
 		true \
 		|| { scripts/mercury_cleanup_install; exit 1; }; \