1 files changed, 5 insertions, 1 deletions
diff --git a/src/projections/urm5.cpp b/src/projections/urm5.cpp
index a93293c0..f89bb1d5 100644
--- a/src/projections/urm5.cpp
+++ b/src/projections/urm5.cpp
@@ -45,7 +45,11 @@ PJ *PROJECTION(urm5) {
     Q->q3 = pj_param(P->ctx, P->params, "dq").f / 3.;
     alpha = pj_param(P->ctx, P->params, "ralpha").f;
     t = Q->n * sin (alpha);
-    Q->m = cos (alpha) / sqrt (1. - t * t);
+    const double denom = sqrt (1. - t * t);
+    if( denom == 0 ) {
+        return pj_default_destructor(P, PJD_ERR_LAT_0_OR_ALPHA_EQ_90);
+    }
+    Q->m = cos (alpha) / denom;
     Q->rmn = 1. / (Q->m * Q->n);
 
     P->es = 0.;