diff --git a/src/calc.rs b/src/calc.rs
index 202e678..e83aeb1 100644
--- a/src/calc.rs
+++ b/src/calc.rs
@@ -283,7 +283,7 @@ impl Calculator {
                     }
                     'E' => {
                         let precision = self.checked_get(0)? as usize;
-                        if precision >= 20 {
+                        if precision > 20 {
                             return Err(CalculatorError::PrecisionTooHigh);
                         }
                         self.display_mode = CalculatorDisplayMode::Engineering(self.pop_usize()?)
@@ -406,6 +406,7 @@ impl Calculator {
         Ok(f)
     }
     pub fn pop_usize(&mut self) -> CalculatorResult<usize> {
+        self.flush_l()?;
         let f = self.checked_get(0)?;
         let ret = f as usize;
         self.direct_state_change(CalculatorStateChange {