diff --git a/src/preprocessing/assertion_pipeline.h b/src/preprocessing/assertion_pipeline.h
index b4aecc9fe35..8d84d5f3685 100644
--- a/src/preprocessing/assertion_pipeline.h
+++ b/src/preprocessing/assertion_pipeline.h
@@ -62,6 +62,10 @@ class AssertionPipeline : protected EnvObj
   /**
    * Adds an assertion/assumption to be preprocessed.
    *
+   * Note that if proofs are provided, a preprocess pass using this method
+   * is required to either provide a proof generator or a trust id that is not
+   * TrustId::UNKNOWN_PREPROCESS_LEMMA.
+   *
    * @param n The assertion/assumption
    * @param isInput If true, n is an input formula (an assumption in the main
    * body of the overall proof).
@@ -91,6 +95,10 @@ class AssertionPipeline : protected EnvObj
    * Replaces assertion i with node n and records the dependency between the
    * original assertion and its replacement.
    *
+   * Note that if proofs are provided, a preprocess pass using this method
+   * is required to either provide a proof generator or a trust id that is not
+   * TrustId::UNKNOWN_PREPROCESS_LEMMA.
+   *
    * @param i The position of the assertion to replace.
    * @param n The replacement assertion.
    * @param pg The proof generator who can provide a proof of d_nodes[i] == n,