diff --git a/bip-0379.md b/bip-0379.md
index 8241bded..a2b5d1fe 100644
--- a/bip-0379.md
+++ b/bip-0379.md
@@ -155,6 +155,10 @@ its type properties in function of those of their subexpressions.
 | `j:X`                        | X is Bn                                               | B           | o=o<sub>X</sub>; n; d; u=u<sub>X</sub>
 | `n:X`                        | X is B                                                | B           | z=z<sub>X</sub>; o=o<sub>X</sub>; n=n<sub>X</sub>; d=d<sub>X</sub>; u
 
+The properties of a fragment assume that the conditions in its "Requires" column are met. They exist
+only to reason about correctness, so they say nothing about an expression that does not meet them:
+such an expression is not valid Miniscript.
+
 #### Timelock Type Mixing
 
 There is one additional correctness property that Miniscript expressions must satisfy:
@@ -207,6 +211,14 @@ The following table lists the malleability properties and requirement of each fr
 | `j:X`                        |                                                                     | s=s<sub>X</sub>; e=f<sub>X
 | `n:X`                        |                                                                     | s=s<sub>X</sub>; f=f<sub>X</sub>; e=e<sub>X</sub>
 
+As in the correctness table, the properties of a fragment assume that the conditions in its
+"Requires" column are met. They exist only to reason about malleability, so they say nothing about
+an expression that does not meet them: such an expression is malleable, and so is every expression
+containing it.
+
+Implementors of APIs which unconditionally return values for these properties should always return
+false for malleable expressions.
+
 ### Satisfaction
 
 The following table shows all valid satisfactions and dissatisfactions for every Miniscript, using