diff --git a/usr.bin/diff/diff.1 b/usr.bin/diff/diff.1
--- a/usr.bin/diff/diff.1
+++ b/usr.bin/diff/diff.1
@@ -396,8 +396,8 @@
 With unified and context diffs, show with each change
 the first 40 characters of the last line before the context beginning
 with a letter, an underscore or a dollar sign.
-For C source code following standard layout conventions, this will
-show the prototype of the function the change applies to.
+For C and Objective-C source code following standard layout conventions, this
+will show the prototype of the function the change applies to.
 .It Fl T -initial-tab
 Print a tab rather than a space before the rest of the line for the
 normal, context or unified output formats.
diff --git a/usr.bin/diff/diffreg.c b/usr.bin/diff/diffreg.c
--- a/usr.bin/diff/diffreg.c
+++ b/usr.bin/diff/diffreg.c
@@ -1419,7 +1419,8 @@
 			strlcpy(lastbuf, buf, sizeof(lastbuf));
 			lastmatchline = pos;
 			return (lastbuf);
-		} else if (isalpha(buf[0]) || buf[0] == '_' || buf[0] == '$') {
+		} else if (isalpha(buf[0]) || buf[0] == '_' || buf[0] == '$'
+			|| buf[0] == '-' || buf[0] == '+') {
 			if (begins_with(buf, "private:")) {
 				if (!state)
 					state = " (private)";
diff --git a/usr.bin/diff/tests/Makefile b/usr.bin/diff/tests/Makefile
--- a/usr.bin/diff/tests/Makefile
+++ b/usr.bin/diff/tests/Makefile
@@ -27,7 +27,14 @@
 	header_ns.out \
 	ifdef.out \
 	group-format.out \
-	strip_o.out
+	strip_o.out \
+	functionname.in \
+	functionname_c.in \
+	functionname_c.out \
+	functionname_objcclassm.in \
+	functionname_objcclassm.out \
+	functionname_objcm.in \
+	functionname_objcm.out
 
 NETBSD_ATF_TESTS_SH+=	netbsd_diff_test
 
diff --git a/usr.bin/diff/tests/diff_test.sh b/usr.bin/diff/tests/diff_test.sh
--- a/usr.bin/diff/tests/diff_test.sh
+++ b/usr.bin/diff/tests/diff_test.sh
@@ -19,6 +19,7 @@
 atf_test_case report_identical
 atf_test_case non_regular_file
 atf_test_case binary
+atf_test_case functionname
 
 simple_body()
 {
@@ -278,6 +279,23 @@
 	atf_check -o inline:"176c\nx\n.\n" -s exit:1 diff -ae A B
 }
 
+functionname_body()
+{
+	atf_check -o empty -x "which diff"
+
+	atf_check -o file:$(atf_get_srcdir)/functionname_c.out -s exit:1 \
+		diff -u -p -L functionname.in -L functionname_c.in \
+		"$(atf_get_srcdir)/functionname.in" "$(atf_get_srcdir)/functionname_c.in"
+
+	atf_check -o file:$(atf_get_srcdir)/functionname_objcm.out -s exit:1 \
+		diff -u -p -L functionname.in -L functionname_objcm.in \
+		"$(atf_get_srcdir)/functionname.in" "$(atf_get_srcdir)/functionname_objcm.in"
+
+	atf_check -o file:$(atf_get_srcdir)/functionname_objcclassm.out -s exit:1 \
+		diff -u -p -L functionname.in -L functionname_objcclassm.in \
+		"$(atf_get_srcdir)/functionname.in" "$(atf_get_srcdir)/functionname_objcclassm.in"
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case simple
@@ -299,4 +317,5 @@
 	atf_add_test_case report_identical
 	atf_add_test_case non_regular_file
 	atf_add_test_case binary
+	atf_add_test_case functionname
 }
diff --git a/usr.bin/diff/tests/functionname.in b/usr.bin/diff/tests/functionname.in
new file mode 100644
--- /dev/null
+++ b/usr.bin/diff/tests/functionname.in
@@ -0,0 +1,29 @@
+static void
+doSomethingThenPrintHello(int test)
+{
+	test = test << 4;
+	if (test % 8 == 6) {
+		return;
+	}
+
+	print("goodbye\n");
+}
+
+
+- (long) readOffset:(FILE*)file
+{
+	if( version >= 11){
+		long offset;
+		fread(&offset, sizeof(long), 1, file);
+		return offset;
+	} else {
+		int offset;
+		fread(&offset, sizeof(int), 1, file);
+		return offset;
+	}
+}
+
++ (BOOL) isEdible:(NSString *)mushroom
+{
+	return TRUE;
+}
diff --git a/usr.bin/diff/tests/functionname_c.in b/usr.bin/diff/tests/functionname_c.in
new file mode 100644
--- /dev/null
+++ b/usr.bin/diff/tests/functionname_c.in
@@ -0,0 +1,29 @@
+static void
+doSomethingThenPrintHello(int test)
+{
+	test = test << 4;
+	if (test % 8 == 6) {
+		return;
+	}
+
+	print("hello\n");
+}
+
+
+- (long) readOffset:(FILE*)file
+{
+	if( version >= 11){
+		long offset;
+		fread(&offset, sizeof(long), 1, file);
+		return offset;
+	} else {
+		int offset;
+		fread(&offset, sizeof(int), 1, file);
+		return offset;
+	}
+}
+
++ (BOOL) isEdible:(NSString *)mushroom
+{
+	return TRUE;
+}
diff --git a/usr.bin/diff/tests/functionname_c.out b/usr.bin/diff/tests/functionname_c.out
new file mode 100644
--- /dev/null
+++ b/usr.bin/diff/tests/functionname_c.out
@@ -0,0 +1,11 @@
+--- functionname.in
++++ functionname_c.in
+@@ -6,7 +6,7 @@ doSomethingThenPrintHello(int test)
+ 		return;
+ 	}
+ 
+-	print("goodbye\n");
++	print("hello\n");
+ }
+ 
+ 
diff --git a/usr.bin/diff/tests/functionname_objcclassm.in b/usr.bin/diff/tests/functionname_objcclassm.in
new file mode 100644
--- /dev/null
+++ b/usr.bin/diff/tests/functionname_objcclassm.in
@@ -0,0 +1,31 @@
+static void
+doSomethingThenPrintHello(int test)
+{
+	test = test << 4;
+	if (test % 8 == 6) {
+		return;
+	}
+
+	print("goodbye\n");
+}
+
+
+- (long) readOffset:(FILE*)file
+{
+	if( version >= 11){
+		long offset;
+		fread(&offset, sizeof(long), 1, file);
+		return offset;
+	} else {
+		int offset;
+		fread(&offset, sizeof(int), 1, file);
+		return offset;
+	}
+}
+
++ (BOOL) isEdible:(NSString *)mushroom
+{
+	/* With a solid guide book (such as Phillips 2006) assume we can't eat
+	 * the fungus */
+	return FALSE;
+}
diff --git a/usr.bin/diff/tests/functionname_objcclassm.out b/usr.bin/diff/tests/functionname_objcclassm.out
new file mode 100644
--- /dev/null
+++ b/usr.bin/diff/tests/functionname_objcclassm.out
@@ -0,0 +1,11 @@
+--- functionname.in
++++ functionname_objcclassm.in
+@@ -25,5 +25,7 @@ + (BOOL) isEdible:(NSString *)mushroom
+ 
+ + (BOOL) isEdible:(NSString *)mushroom
+ {
+-	return TRUE;
++	/* With a solid guide book (such as Phillips 2006) assume we can't eat
++	 * the fungus */
++	return FALSE;
+ }
diff --git a/usr.bin/diff/tests/functionname_objcm.in b/usr.bin/diff/tests/functionname_objcm.in
new file mode 100644
--- /dev/null
+++ b/usr.bin/diff/tests/functionname_objcm.in
@@ -0,0 +1,29 @@
+static void
+doSomethingThenPrintHello(int test)
+{
+	test = test << 4;
+	if (test % 8 == 6) {
+		return;
+	}
+
+	print("goodbye\n");
+}
+
+
+- (long) readOffset:(FILE*)file
+{
+	if( version >= 11){
+		long offset;
+		fread(&offset, sizeof(long), 1, file);
+		return offset;
+	} else {
+		int offset;
+		fread(&offset-1, sizeof(int), 1, file);
+		return offset;
+	}
+}
+
++ (BOOL) isEdible:(NSString *)mushroom
+{
+	return TRUE;
+}
diff --git a/usr.bin/diff/tests/functionname_objcm.out b/usr.bin/diff/tests/functionname_objcm.out
new file mode 100644
--- /dev/null
+++ b/usr.bin/diff/tests/functionname_objcm.out
@@ -0,0 +1,11 @@
+--- functionname.in
++++ functionname_objcm.in
+@@ -18,7 +18,7 @@ - (long) readOffset:(FILE*)file
+ 		return offset;
+ 	} else {
+ 		int offset;
+-		fread(&offset, sizeof(int), 1, file);
++		fread(&offset-1, sizeof(int), 1, file);
+ 		return offset;
+ 	}
+ }