diff --git a/arch/mips/ksigaction.h b/arch/mips/ksigaction.h
index 648ce0685bae6043f636a50a46c5d744adf14b4f..6d731646c14235e8bff19884301ec1569dce1cf0 100644
--- a/arch/mips/ksigaction.h
+++ b/arch/mips/ksigaction.h
@@ -2,5 +2,8 @@ struct k_sigaction {
 	unsigned flags;
 	void (*handler)(int);
 	unsigned long mask[4];
+	/* The following field is past the end of the structure the
+	 * kernel will read or write, and exists only to avoid having
+	 * mips-specific preprocessor conditionals in sigaction.c. */
 	void (*restorer)();
 };
diff --git a/src/internal/ksigaction.h b/src/internal/ksigaction.h
index 9a70f93798bfb9c3fac835e931eb87290402ae38..2eacabf1138e122c71e6dc3aaa1d477cd4a03f06 100644
--- a/src/internal/ksigaction.h
+++ b/src/internal/ksigaction.h
@@ -1,3 +1,6 @@
+/* This is the structure used for the rt_sigaction syscall on most archs,
+ * but it can be overridden by a file with the same name in the top-level
+ * arch dir for a given arch, if necessary. */
 struct k_sigaction {
 	void (*handler)(int);
 	unsigned long flags;