diff --git a/CMakeLists.txt b/CMakeLists.txt
index 30008d6..c9f1912 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,10 +23,11 @@ ENDIF(NOT WIN32)
 ADD_SUBDIRECTORY(avida-core)

 # Default location for installed software/configs/ docs is the build directory.
+IF(NOT CMAKE_INSTALL_PREFIX)
 SET(CMAKE_INSTALL_PREFIX
   "${PROJECT_BINARY_DIR}"
   CACHE PATH
   "Install path prefix, prepended onto install directories."
   FORCE
 )
-
+ENDIF(NOT CMAKE_INSTALL_PREFIX)
diff --git a/avida-core/CMakeLists.txt b/avida-core/CMakeLists.txt
index d9d063e..30c4f6a 100644
--- a/avida-core/CMakeLists.txt
+++ b/avida-core/CMakeLists.txt
@@ -12,13 +12,14 @@ ENDIF(COMMAND cmake_policy)
 # PROJECT_BINARY_DIR, since the project didn't exist yet.

 # Default location for installed software/configs/ docs is the build directory.
+IF(NOT CMAKE_INSTALL_PREFIX)
 SET(CMAKE_INSTALL_PREFIX
   "${PROJECT_BINARY_DIR}"
   CACHE PATH
   "Install path prefix, prepended onto install directories."
   FORCE
 )
-
+ENDIF(NOT CMAKE_INSTALL_PREFIX)
 # Final software is built directly into the work subdirectory.
 SET(EXECUTABLE_OUTPUT_PATH
   "${PROJECT_BINARY_DIR}/bin"
diff --git a/libs/tcmalloc-1.4/CMakeLists.txt b/libs/tcmalloc-1.4/CMakeLists.txt
index 59f8f1a..54873b1 100644
--- a/libs/tcmalloc-1.4/CMakeLists.txt
+++ b/libs/tcmalloc-1.4/CMakeLists.txt
@@ -3,13 +3,14 @@ PROJECT(TCMALLOC CXX)
 CMAKE_MINIMUM_REQUIRED(VERSION 2.6)

 # Default location for installed software/configs/ docs is the build directory.
+IF(NOT CMAKE_INSTALL_PREFIX)
 SET(CMAKE_INSTALL_PREFIX
   "${PROJECT_BINARY_DIR}"
   CACHE PATH
   "Install path prefix, prepended onto install directories."
   FORCE
 )
-
+ENDIF(NOT CMAKE_INSTALL_PREFIX)
 # Final software is built directly into the work subdirectory.
 SET(EXECUTABLE_OUTPUT_PATH
   "${PROJECT_BINARY_DIR}/bin"