diff --git a/.gitignore b/.gitignore
index 319d66928..ad141138e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 
 build/*
+_codeql_build_dir/
 
 Makefile
 *.lo
diff --git a/_codeql_detected_source_root b/_codeql_detected_source_root
new file mode 120000
index 000000000..945c9b46d
--- /dev/null
+++ b/_codeql_detected_source_root
@@ -0,0 +1 @@
+.
\ No newline at end of file
diff --git a/expui/BiorthBasis.cc b/expui/BiorthBasis.cc
index b3e07b243..e718d9f2f 100644
--- a/expui/BiorthBasis.cc
+++ b/expui/BiorthBasis.cc
@@ -1558,6 +1558,17 @@ namespace BasisClasses
     pnum = std::max<int>(1,  pnum);
     tnum = std::max<int>(10, tnum);
     
+    // Validate bias parameter
+    //
+    if (!std::isfinite(bias)) {
+      throw std::runtime_error("Cylindrical: 'bias' parameter must be finite");
+    }
+    if (bias <= 0.0) {
+      std::ostringstream sout;
+      sout << "Cylindrical: 'bias' parameter must be positive, got " << bias;
+      throw std::runtime_error(sout.str());
+    }
+    
     EmpCylSL::RMIN        = rcylmin;
     EmpCylSL::RMAX        = rcylmax;
     EmpCylSL::NUMX        = ncylnx;