diff --git a/base/expr.jl b/base/expr.jl
index 75e54a2249508..284beed95c9a4 100644
--- a/base/expr.jl
+++ b/base/expr.jl
@@ -388,13 +388,14 @@ macro constprop(setting)
 end
 
 function constprop_setting(@nospecialize setting)
+    s = setting
     isa(setting, QuoteNode) && (setting = setting.value)
     if setting === :aggressive
         return :aggressive_constprop
     elseif setting === :none
         return :no_constprop
     end
-    throw(ArgumentError(LazyString("@constprop "), setting, "not supported"))
+    throw(ArgumentError(LazyString("`Base.@constprop ", s, "` not supported")))
 end
 
 """
diff --git a/test/misc.jl b/test/misc.jl
index 79b684badf1e0..c4a12c4db8e7d 100644
--- a/test/misc.jl
+++ b/test/misc.jl
@@ -1402,3 +1402,15 @@ end
     GC.gc(true); yield()
     @test in_fin[]
 end
+
+@testset "`@constprop`, `@assume_effects` handling of an unknown setting" begin
+    for x ∈ ("constprop", "assume_effects")
+        try
+            eval(Meta.parse("Base.@$x :unknown f() = 3"))
+            error("unexpectedly reached")
+        catch e
+            e::LoadError
+            @test e.error isa ArgumentError
+        end
+    end
+end