diff --git a/src/preserves.nim b/src/preserves.nim
index 6ad3862..22a845e 100644
--- a/src/preserves.nim
+++ b/src/preserves.nim
@@ -650,7 +650,9 @@ template preservesLiteral*(value: typed) {.pragma.}
 
 template unpreservable*() {.pragma.}
   ## Pragma to forbid a type from being converted by ``toPreserve``.
-  ## See ``toPreserve``.
+  ## Useful for preventing an embeded type from being encoded
+  ## as its native type.
+  ## Unpreservability is asserted at runtime.
 
 proc toPreserve*[T](x: T; E = void): Preserve[E] =
   ## Serializes ``x`` to Preserves. Can be customized by defining
@@ -704,7 +706,8 @@ proc toPreserve*[T](x: T; E = void): Preserve[E] =
         cast[Preserve[E]](lit)
       else:
         toPreserve(val, E)
-    when T.hasCustomPragma(unpreservable): {.fatal: "unpreservable type".}
+    when T.hasCustomPragma(unpreservable):
+      raiseAssert($T & " is unpreservable")
     elif T.hasCustomPragma(preservesOr):
       var hasKind, hasVariant: bool
       for k, v in x.fieldPairs:
@@ -891,7 +894,8 @@ proc fromPreserve*[T, E](v: var T; pr: Preserve[E]): bool =
         pr == lit
       else:
         fromPreserve(val, pr)
-    when T.hasCustomPragma(unpreservable): {.fatal: "unpreservable type " & $T.}
+    when T.hasCustomPragma(unpreservable):
+      raiseAssert($T & " is unpreservable")
     elif T.hasCustomPragma(preservesRecord):
       if pr.isRecord and pr.label.isSymbol(T.getCustomPragmaVal(preservesRecord)):
         result = true