diff --git a/common/src/aaredaqlib/diffraction_geometry.py b/common/src/aaredaqlib/diffraction_geometry.py
index 3a1f1219..850b7fac 100644
--- a/common/src/aaredaqlib/diffraction_geometry.py
+++ b/common/src/aaredaqlib/diffraction_geometry.py
@@ -42,6 +42,8 @@ class DiffractionGeometry(BaseModel):
     def calc_dtz_mm(self, exp_resolution_angstrom: float) -> float:
         if exp_resolution_angstrom <= 0:
             raise ValueError("Resolution must be positive")
-
-        theta = math.asin(self.wavelength_angstrom / (2 * exp_resolution_angstrom))
+        x = self.wavelength_angstrom / (2 * exp_resolution_angstrom)
+        if x >= 1.0 or x <= -1.0:
+            return 0.0
+        theta = math.asin(x)
         return self.detector_radius_mm / math.tan(theta)
\ No newline at end of file