diff --git a/CMakeLists.txt b/CMakeLists.txt
index c2c527a..a7796fd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,18 @@
 cmake_minimum_required(VERSION 2.8.5)
 
+# Make sure the user doesn't play dirty with symlinks
+get_filename_component(srcdir "${CMAKE_SOURCE_DIR}" REALPATH)
+get_filename_component(bindir "${CMAKE_BINARY_DIR}" REALPATH)
+
+# Disallow in-source builds
+if(${srcdir} STREQUAL ${bindir})
+ message(FATAL_ERROR "In-source builds are not allowed."
+ " Please create a directory and run cmake from there, passing the path"
+ " to this source directory as the last argument. This process created"
+ " the file `CMakeCache.txt' and the directory `CMakeFiles' in ${srcdir}."
+ " Please remove them.")
+endif()
+
 project(gmt_makemap CXX)
 
 if(NOT CMAKE_BUILD_TYPE)