diff --git a/Makefile.am b/Makefile.am
index 4fc84c1d..168d9fe6 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -378,6 +378,7 @@ noinst_HEADERS = \
     sbr/fmt_new.h \
     sbr/fmt_rfc2047.h \
     sbr/fmt_scan.h \
+    sbr/fold.h \
     sbr/folder_addmsg.h \
     sbr/folder_delmsgs.h \
     sbr/folder_free.h \
@@ -1106,6 +1107,7 @@ sbr_libmh_a_SOURCES = \
     sbr/fmt_new.c \
     sbr/fmt_rfc2047.c \
     sbr/fmt_scan.c \
+    sbr/fold.c \
     sbr/folder_addmsg.c \
     sbr/folder_delmsgs.c \
     sbr/folder_free.c \
diff --git a/sbr/fold.c b/sbr/fold.c
new file mode 100644
index 00000000..d80cfe2d
--- /dev/null
+++ b/sbr/fold.c
@@ -0,0 +1,63 @@
+/* fold.c -- fold a mail header field
+ *
+ * This code is Copyright (c), by the authors of nmh.  See the
+ * COPYRIGHT file in the root directory of the nmh distribution for
+ * complete copyright information. */
+
+#include "h/mh.h"
+#include "h/mime.h"
+#include "sbr/charstring.h"
+#include "fold.h"
+
+void
+fold(charstring_t dst, size_t namelen, const char *restrict body)
+{
+	const char *restrict body_next;
+	const char *restrict wsp;
+	const char *restrict wsp_next;
+	const bool crlf = strchr(body, '\r');
+	charstring_clear(dst);
+	namelen++;
+
+	while (*body) {
+		body_next = strchr(body, '\n');
+		if ((unsigned long) (body_next - body) <= MAXTEXTPERLN - namelen) {
+			charstring_push_back_chars(dst, body, body_next - body + 1, body_next - body + 1);
+			namelen = 0;
+			body = body_next + 1;
+			continue;
+		}
+		wsp = body;
+		while (namelen == 0 && (*wsp == ' ' || *wsp == '\t')) {
+			wsp++;
+		}
+		wsp = wsp_next = strpbrk(wsp, " \t");
+
+		/* if now whitespace is in the current line just print the curret line as is */
+		if (!wsp_next || wsp_next > body_next) {
+			charstring_push_back_chars(dst, body, body_next - body + 1, body_next - body + 1);
+			namelen = 0;
+			body = body_next + 1;
+			continue;
+		}
+
+		while ((unsigned long)(wsp_next - body) <= MAXTEXTPERLN - namelen) {
+			wsp = wsp_next;
+			wsp_next = strpbrk(wsp+1, " \t");
+			if (!wsp_next) {
+				break;
+			}
+			if (wsp_next > body_next) {
+				break;
+			}
+		}
+
+		charstring_push_back_chars(dst, body, wsp - body, wsp - body);
+		if (crlf) {
+			charstring_push_back(dst, '\r');
+		}
+		charstring_push_back(dst, '\n');
+		namelen = 0;
+		body = wsp;
+	}
+}
diff --git a/sbr/fold.h b/sbr/fold.h
new file mode 100644
index 00000000..8d0fd6d7
--- /dev/null
+++ b/sbr/fold.h
@@ -0,0 +1,7 @@
+/* fold.h -- fold a mail header field
+ *
+ * This code is Copyright (c), by the authors of nmh.  See the
+ * COPYRIGHT file in the root directory of the nmh distribution for
+ * complete copyright information. */
+
+void fold(charstring_t dst, size_t namelen, const char *restrict body);
diff --git a/test/mhbuild/test-mhbuild b/test/mhbuild/test-mhbuild
index 706a804a..f8d4992b 100755
--- a/test/mhbuild/test-mhbuild
+++ b/test/mhbuild/test-mhbuild
@@ -221,5 +221,58 @@ run_test "mhbuild $f" \
 
 check "$f" "$expected"
 
+start_test "Checking for correct header folding"
+
+cat >"`mhpath new`" <<\E
+From: Somebody <somebody@example.com>
+To: Nobody <nobody@example.com>
+Subject: Test message
+References: <aaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com> <aaaaaaaaaaaaaaaaaaaaaaaaaab@example.com> <c@example.com>
+--------
+This is a test
+E
+
+cat > "$expected" <<\E
+From: Somebody <somebody@example.com>
+To: Nobody <nobody@example.com>
+Subject: Test message
+References: <aaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com>
+ <aaaaaaaaaaaaaaaaaaaaaaaaaab@example.com> <c@example.com>
+MIME-Version: 1.0
+Content-Type: text/plain; charset="us-ascii"
+
+This is a test
+E
+
+run_test "mhbuild -auto `mhpath last`"
+check "`mhpath last`" "$expected"
+
+start_test "Checking header folding with a to long line"
+
+cat >"`mhpath new`" <<\E
+From: Somebody <somebody@example.com>
+To: Nobody <nobody@example.com>
+Subject: Test message
+References: <aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com>  <aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com>
+--------
+This is a test
+E
+
+cat > "$expected" <<\E
+From: Somebody <somebody@example.com>
+To: Nobody <nobody@example.com>
+Subject: Test message
+References:
+ <aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com>
+  <aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com>
+MIME-Version: 1.0
+Content-Type: text/plain; charset="us-ascii"
+
+This is a test
+E
+
+run_test "mhbuild -auto `mhpath last`"
+check "`mhpath last`" "$expected"
+
 finish_test
 exit $failed
diff --git a/uip/mhoutsbr.c b/uip/mhoutsbr.c
index 6033cad8..6f80bafc 100644
--- a/uip/mhoutsbr.c
+++ b/uip/mhoutsbr.c
@@ -17,6 +17,8 @@
 #include "h/mhparse.h"
 #include "mhoutsbr.h"
 #include "sbr/base64.h"
+#include "sbr/charstring.h"
+#include "sbr/fold.h"
 
 
 /*
@@ -199,12 +201,15 @@ static void
 output_headers (CT ct, FILE *out)
 {
     HF hp;
+    charstring_t body = charstring_create(0);
 
     hp = ct->c_first_hf;
     while (hp) {
-	fprintf (out, "%s:%s", hp->name, hp->value);
+	fold (body, strlen(hp->name), hp->value);
+	fprintf (out, "%s:%s", hp->name, charstring_buffer(body));
 	hp = hp->next;
     }
+    charstring_free(body);
 }