diff --git a/source_text.lua b/source_text.lua
index c28e203..dac2820 100644
--- a/source_text.lua
+++ b/source_text.lua
@@ -974,9 +974,8 @@ function Text.offset(s, pos1)
   if pos1 == 1 then return 1 end
   local result = utf8.offset(s, pos1)
   if result == nil then
-    print(pos1, #s, s)
+    assert(false, ('Text.offset(%d) called on a string of length %d (byte size %d); this is likely a failure to handle utf8\n\n^%s$\n'):format(pos1, utf8.len(s), #s, s))
   end
-  assert(result, "Text.offset returned nil; this is likely a failure to handle utf8")
   return result
 end
 
diff --git a/text.lua b/text.lua
index 33dd29e..f1f6e48 100644
--- a/text.lua
+++ b/text.lua
@@ -835,9 +835,8 @@ function Text.offset(s, pos1)
   if pos1 == 1 then return 1 end
   local result = utf8.offset(s, pos1)
   if result == nil then
-    print(pos1, #s, s)
+    assert(false, ('Text.offset(%d) called on a string of length %d (byte size %d); this is likely a failure to handle utf8\n\n^%s$\n'):format(pos1, utf8.len(s), #s, s))
   end
-  assert(result, "Text.offset returned nil; this is likely a failure to handle utf8")
   return result
 end