diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8b47843c..f7593b28 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -89,6 +89,11 @@ if (BUILD_WITH_W3EMC)
   endif()
 endif()
 
+# We need g2c if G2C_COMPARE is chosen.
+if (G2C_COMPARE)
+  find_package(g2c 1.7.0 REQUIRED)
+endif()
+
 # Figure whether user wants a _4, a _d, or both libraries.
 if(BUILD_4 AND BUILD_D)
   set(kinds "4" "d")