diff --git a/src/compat/assumptions.h b/src/compat/assumptions.h
--- a/src/compat/assumptions.h
+++ b/src/compat/assumptions.h
@@ -64,4 +64,17 @@
 // * We are NOT assuming a specific value for
 // std::numeric_limits<char>::is_signed.
 
+/**
+ * /!\ C++ right shift signedness handling is implementation defined. It is
+ *     defined as an arithmetic on all the platform we support, but this
+ *     may not be the case on other platforms.
+ *
+ * NB: C++20 defines signed right shift as being arithmetic shifts, so in
+ * practice, we should see all platforms converge toward that behavior if
+ * they haven't already.
+ */
+static_assert(
+    (int64_t(-1) >> 1) == int64_t(-1),
+    "deterministicExp2 require a compiler using arithmetic right shift.");
+
 #endif // BITCOIN_COMPAT_ASSUMPTIONS_H