diff --git a/common.scad b/common.scad
index eebd141..51d8363 100644
--- a/common.scad
+++ b/common.scad
@@ -289,13 +289,28 @@ function get_anchor(anchor,center,uncentered=BOT,dflt=CENTER) =
 //   d = Most general diameter.
 //   dflt = Value to return if all other values given are `undef`.
 function get_radius(r1=undef, r2=undef, r=undef, d1=undef, d2=undef, d=undef, dflt=undef) = (
-    !is_undef(r1)? assert(is_undef(r2)&&is_undef(d1)&&is_undef(d2), "Conflicting or redundant radius/diameter arguments given.") r1 :
-    !is_undef(r2)? assert(is_undef(d1)&&is_undef(d2), "Conflicting or redundant radius/diameter arguments given.") r2 :
-    !is_undef(d1)? d1/2 :
-    !is_undef(d2)? d2/2 :
-    !is_undef(r)? assert(is_undef(d), "Conflicting or redundant radius/diameter arguments given.") r :
-    !is_undef(d)? d/2 :
-    dflt
+    !is_undef(r1)
+		? assert(is_undef(r2)&&is_undef(d1)&&is_undef(d2), "Conflicting or redundant radius/diameter arguments given.") 
+				assert(is_finite(r1), "Invalid radius r1." )
+				r1 
+    : !is_undef(r2)
+			? assert(is_undef(d1)&&is_undef(d2), "Conflicting or redundant radius/diameter arguments given.") 
+				assert(is_finite(r2), "Invalid radius r2." )
+				r2
+		: !is_undef(d1)
+		  ? assert(is_finite(d1), "Invalid diameter d1." )
+				d1/2
+		: !is_undef(d2)
+			? assert(is_finite(d2), "Invalid diameter d2." )
+				d2/2
+		: !is_undef(r)
+			? assert(is_undef(d), "Conflicting or redundant radius/diameter arguments given.")
+				assert(is_finite(r) || is_vector(r,1) || is_vector(r,2), "Invalid radius r." )
+				r 
+		: !is_undef(d)
+			? assert(is_finite(d) || is_vector(d,1) || is_vector(d,2), "Invalid diameter d." )
+			d/2
+		: dflt
 );
 
 // Function: get_height()