diff -ur InsightToolkit-4.13.2/Modules/ThirdParty/libLBFGS/src/CMakeLists.txt InsightToolkit-4.13.2_fix/Modules/ThirdParty/libLBFGS/src/CMakeLists.txt
--- InsightToolkit-4.13.2/Modules/ThirdParty/libLBFGS/src/CMakeLists.txt	2019-02-28 17:45:49.000000000 +0100
+++ InsightToolkit-4.13.2_fix/Modules/ThirdParty/libLBFGS/src/CMakeLists.txt	2019-07-02 16:05:59.161006477 +0200
@@ -17,6 +17,8 @@
 set(ITK3P_INSTALL_LIBRARY_DIR "${ITKLIBLBFGS_INSTALL_LIBRARY_DIR}")
 set(ITK3P_INSTALL_ARCHIVE_DIR "${ITKLIBLBFGS_INSTALL_ARCHIVE_DIR}")
 
+TARGET_LINK_LIBRARIES(itklbfgs -lm)
+
 INSTALL(TARGETS itklbfgs
   EXPORT ${ITK3P_INSTALL_EXPORT_NAME}
   RUNTIME DESTINATION ${ITK3P_INSTALL_RUNTIME_DIR} COMPONENT RuntimeLibraries