diff --git a/configure.ac b/configure.ac
index 1530ecf..e4aa911 100644
--- a/configure.ac
+++ b/configure.ac
@@ -30,6 +30,7 @@ LT_INIT
 LIBMD_LINKER_VERSION_SCRIPT
 
 # Checks for programs.
+AC_PROG_SED
 AC_PROG_CC
 
 # Checks for the build machinery.
diff --git a/man/Makefile.am b/man/Makefile.am
index a919705..0e05213 100644
--- a/man/Makefile.am
+++ b/man/Makefile.am
@@ -12,13 +12,13 @@ SED_MD4_SUBST = -e 's/mdX/md4/g' -e 's/MDX/MD4/g'
 SED_MD5_SUBST = -e 's/mdX/md5/g' -e 's/MDX/MD5/g'
 
 md2.3: $(srcdir)/mdX.3
-	$(AM_V_GEN) sed $(SED_MD2_SUBST) $< >$@
+	$(AM_V_GEN) $(SED) $(SED_MD2_SUBST) $< >$@
 
 md4.3: $(srcdir)/mdX.3
-	$(AM_V_GEN) sed $(SED_MD4_SUBST) $< >$@
+	$(AM_V_GEN) $(SED) $(SED_MD4_SUBST) $< >$@
 
 md5.3: $(srcdir)/mdX.3
-	$(AM_V_GEN) sed $(SED_MD5_SUBST) $< >$@
+	$(AM_V_GEN) $(SED) $(SED_MD5_SUBST) $< >$@
 
 dist_man_MANS = \
 	md2.3 \
diff --git a/src/Makefile.am b/src/Makefile.am
index 341867a..2f3f555 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -74,33 +74,33 @@ DISTCLEANFILES = \
 # Generate a simple libtool symbol export list to be used as a fallback if
 # there is no version script support.
 libmd.sym: libmd.map
-	$(AM_V_GEN) sed -ne 's/^[[:space:]]\{1,\}\([A-Za-z0-9]\{1,\}\);/\1/p' $< > $@
+	$(AM_V_GEN) $(SED) -ne 's/^[[:space:]]\{1,\}\([A-Za-z0-9]\{1,\}\);/\1/p' $< > $@
 
 md2hl.c: helper.c
-	$(AM_V_GEN) sed -e 's/hashinc/md2.h/g' -e 's/HASH/MD2/g' $< > $@
+	$(AM_V_GEN) $(SED) -e 's/hashinc/md2.h/g' -e 's/HASH/MD2/g' $< > $@
 
 md4hl.c: helper.c
-	$(AM_V_GEN) sed -e 's/hashinc/md4.h/g' -e 's/HASH/MD4/g' $< > $@
+	$(AM_V_GEN) $(SED) -e 's/hashinc/md4.h/g' -e 's/HASH/MD4/g' $< > $@
 
 md5hl.c: helper.c
-	$(AM_V_GEN) sed -e 's/hashinc/md5.h/g' -e 's/HASH/MD5/g' $< > $@
+	$(AM_V_GEN) $(SED) -e 's/hashinc/md5.h/g' -e 's/HASH/MD5/g' $< > $@
 
 rmd160hl.c: helper.c
-	$(AM_V_GEN) sed -e 's/hashinc/rmd160.h/g' -e 's/HASH/RMD160/g' $< > $@
+	$(AM_V_GEN) $(SED) -e 's/hashinc/rmd160.h/g' -e 's/HASH/RMD160/g' $< > $@
 
 sha1hl.c: helper.c
-	$(AM_V_GEN) sed -e 's/hashinc/sha1.h/g' -e 's/HASH/SHA1/g' $< > $@
+	$(AM_V_GEN) $(SED) -e 's/hashinc/sha1.h/g' -e 's/HASH/SHA1/g' $< > $@
 
 sha256hl.c: helper.c
-	$(AM_V_GEN) sed -e 's/hashinc/sha2.h/g' -e 's/HASH/SHA256/g' \
+	$(AM_V_GEN) $(SED) -e 's/hashinc/sha2.h/g' -e 's/HASH/SHA256/g' \
 	                -e 's/SHA[0-9][0-9][0-9]_CTX/SHA2_CTX/g' $< > $@
 
 sha384hl.c: helper.c
-	$(AM_V_GEN) sed -e 's/hashinc/sha2.h/g' -e 's/HASH/SHA384/g' \
+	$(AM_V_GEN) $(SED) -e 's/hashinc/sha2.h/g' -e 's/HASH/SHA384/g' \
 	                -e 's/SHA[0-9][0-9][0-9]_CTX/SHA2_CTX/g' $< > $@
 
 sha512hl.c: helper.c
-	$(AM_V_GEN) sed -e 's/hashinc/sha2.h/g' -e 's/HASH/SHA512/g' \
+	$(AM_V_GEN) $(SED) -e 's/hashinc/sha2.h/g' -e 's/HASH/SHA512/g' \
 	                -e 's/SHA[0-9][0-9][0-9]_CTX/SHA2_CTX/g' $< > $@
 
 runtimelibdir = $(libdir)
@@ -111,7 +111,7 @@ install-exec-hook:
 		mv $(DESTDIR)$(libdir)/libmd*.so.* \
 		   $(DESTDIR)$(runtimelibdir)/; \
 		soname=`readlink $(DESTDIR)$(libdir)/libmd.so`; \
-		sorelprefix=`echo $(libdir) | sed -r -e 's:(^/)?[^/]+:..:g'`; \
+		sorelprefix=`echo $(libdir) | $(SED) -r -e 's:(^/)?[^/]+:..:g'`; \
 		ln -sf $$sorelprefix$(runtimelibdir)/$$soname \
 		       $(DESTDIR)$(libdir)/libmd.so; \
 	fi