diff -up gl2ps-1.4.2/CMakeLists.txt.lm gl2ps-1.4.2/CMakeLists.txt
--- gl2ps-1.4.2/CMakeLists.txt.lm	2020-07-03 18:01:03.480340544 +0200
+++ gl2ps-1.4.2/CMakeLists.txt	2020-07-03 18:02:15.123852223 +0200
@@ -128,6 +128,8 @@ endif()
 
 include_directories(${EXTERNAL_INCLUDES})
 
+list(APPEND EXTERNAL_LIBRARIES -lm)
+
 if(APPLE)
   # OpenGL and GLUT are deprecated on macOS...
   include(CheckCCompilerFlag)