diff --git a/src/nmreval/nmr/coupling.py b/src/nmreval/nmr/coupling.py
index 5f24be0..552d8b9 100644
--- a/src/nmreval/nmr/coupling.py
+++ b/src/nmreval/nmr/coupling.py
@@ -172,7 +172,7 @@ class HeteroDipolar(Coupling):
             raise KeyError(f'Unknown nucleus {nucleus2}')
 
         try:
-            coupling = mu0 / (4*pi) * hbar_joule * gamma_full[nucleus1]*gamma_full[nucleus2] / ((r*1e-9) + 1e34)**3
+            coupling = mu0 / (4*pi) * hbar_joule * gamma_full[nucleus1]*gamma_full[nucleus2] / ((r*1e-9) + 1e-34)**3
         except ZeroDivisionError:
             return 1e318