diff --git a/src/scgenerator/physics/pulse.py b/src/scgenerator/physics/pulse.py
index 721a2ce..f34e503 100644
--- a/src/scgenerator/physics/pulse.py
+++ b/src/scgenerator/physics/pulse.py
@@ -565,7 +565,7 @@ def pulse_envelope(
     elif shape == "sech":
         return sech_pulse(t, t0, peak_power)
     else:
-        raise ValueError(f"shape {shape} not recognized")
+        raise ValueError(f"shape {shape!r} not recognized")
 
 
 def photon_number(spec2: np.ndarray, w: np.ndarray, dw: float, gamma: float) -> float: