diff --git a/contrib/lax_der_parsing.h b/contrib/lax_der_parsing.h
index 5cb3222..034a38e 100644
--- a/contrib/lax_der_parsing.h
+++ b/contrib/lax_der_parsing.h
@@ -51,6 +51,10 @@
 #ifndef SECP256K1_CONTRIB_LAX_DER_PARSING_H
 #define SECP256K1_CONTRIB_LAX_DER_PARSING_H
 
+/* #include secp256k1.h only when it hasn't been included yet.
+   This enables this file to be #included directly in other project
+   files (such as tests.c) without the need to set an explicit -I flag,
+   which would be necessary to locate secp256k1.h. */
 #ifndef SECP256K1_H
 #include <secp256k1.h>
 #endif
diff --git a/contrib/lax_der_privatekey_parsing.h b/contrib/lax_der_privatekey_parsing.h
index a397f0f..1a8ad8a 100644
--- a/contrib/lax_der_privatekey_parsing.h
+++ b/contrib/lax_der_privatekey_parsing.h
@@ -28,6 +28,10 @@
 #ifndef SECP256K1_CONTRIB_BER_PRIVATEKEY_H
 #define SECP256K1_CONTRIB_BER_PRIVATEKEY_H
 
+/* #include secp256k1.h only when it hasn't been included yet.
+   This enables this file to be #included directly in other project
+   files (such as tests.c) without the need to set an explicit -I flag,
+   which would be necessary to locate secp256k1.h. */
 #ifndef SECP256K1_H
 #include <secp256k1.h>
 #endif