diff --git a/doc/Makefile.am b/doc/Makefile.am
index 224bcd8fc..c151333cd 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -30,13 +30,12 @@ EXTRA_DIST = perm.texi getdate.texi constants.texi fdl.texi
 AM_MAKEINFOFLAGS = --no-split
 
 constants.texi: $(top_srcdir)/src/tail.c $(top_srcdir)/src/shred.c
-	LC_ALL=C \
-	sed -n -e 's/^#define \(DEFAULT_MAX[_A-Z]*\) \(.*\)/@set \1 \2/p' \
-	  $(top_srcdir)/src/tail.c > t-$@
-	LC_ALL=C \
-	sed -n -e 's/.*\(DEFAULT_PASSES\)[ =]* \([0-9]*\).*/@set SHRED_\1 \2/p'\
-	  $(top_srcdir)/src/shred.c >> t-$@
-	mv t-$@ $@
+	$(AM_V_GEN)LC_ALL=C; export LC_ALL; \
+	{ sed -n -e 's/^#define \(DEFAULT_MAX[_A-Z]*\) \(.*\)/@set \1 \2/p' \
+	    $(top_srcdir)/src/tail.c && \
+	  sed -n -e 's/.*\(DEFAULT_PASSES\)[ =]* \([0-9]*\).*/@set SHRED_\1 \2/p'\
+	    $(top_srcdir)/src/shred.c; } > t-$@ \
+	  && mv t-$@ $@
 
 MAINTAINERCLEANFILES = constants.texi