diff --git a/configure.ac b/configure.ac
index 5af8aa5818..b21fd44800 100644
--- a/configure.ac
+++ b/configure.ac
@@ -136,6 +136,10 @@ AC_CHECK_HEADERS([locale], [], [], [])
 AC_LANG_POP(C++)
 
 
+# Check for <err.h>.
+AC_CHECK_HEADER([err.h], [], [bsddiff_compat_include="-Icompat-include"])
+AC_SUBST([bsddiff_compat_include])
+
 # Check whether we have the personality() syscall, which allows us to
 # do i686-linux builds on x86_64-linux machines.
 AC_CHECK_HEADERS([sys/personality.h])
diff --git a/src/bsdiff-4.3/Makefile.am b/src/bsdiff-4.3/Makefile.am
index 4b3af07837..953139f559 100644
--- a/src/bsdiff-4.3/Makefile.am
+++ b/src/bsdiff-4.3/Makefile.am
@@ -8,4 +8,4 @@ bspatch_SOURCES = bspatch.c
 
 bspatch_LDADD = ${bzip2_lib}
 
-AM_CFLAGS = -O3 ${bzip2_include}
+AM_CFLAGS = -O3 ${bzip2_include} ${bsddiff_compat_include}
diff --git a/src/bsdiff-4.3/compat-include/err.h b/src/bsdiff-4.3/compat-include/err.h
new file mode 100644
index 0000000000..a851ded6f9
--- /dev/null
+++ b/src/bsdiff-4.3/compat-include/err.h
@@ -0,0 +1,12 @@
+/* Simulate BSD's <err.h> functionality. */
+
+#ifndef COMPAT_ERR_H_INCLUDED
+#define COMPAT_ERR_H_INCLUDED 1
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define err(rc,...)  do { fprintf(stderr,__VA_ARGS__); exit(rc); } while(0)
+#define errx(rc,...) do { fprintf(stderr,__VA_ARGS__); exit(rc); } while(0)
+
+#endif