diff --git a/.travis.yml b/.travis.yml
index ff6756292..f669e3ae6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -18,6 +18,7 @@ matrix:
                       - libxcursor-dev
                       - libxi-dev
                       - libxext-dev
+                      - libx11-dev
           env:
               - BUILD_SHARED_LIBS=ON
               - CFLAGS=-Werror
@@ -32,6 +33,7 @@ matrix:
                       - libxcursor-dev
                       - libxi-dev
                       - libxext-dev
+                      - libx11-dev
           env:
               - BUILD_SHARED_LIBS=OFF
               - CFLAGS=-Werror
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 59ab473c9..aa171f29f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -158,6 +158,10 @@ if (_GLFW_X11)
     # Set up library and include paths
     list(APPEND glfw_INCLUDE_DIRS "${X11_X11_INCLUDE_PATH}")
 
+    if (NOT X11_X11_INCLUDE_PATH)
+        message(FATAL_ERROR "X111 headers not found; install libx11 development package")
+    endif()
+
     # Check for XRandR (modern resolution switching and gamma control)
     if (NOT X11_Xrandr_INCLUDE_PATH)
         message(FATAL_ERROR "RandR headers not found; install libxrandr development package")
@@ -187,6 +191,8 @@ if (_GLFW_X11)
     if (NOT X11_Xshape_INCLUDE_PATH)
         message(FATAL_ERROR "X Shape headers not found; install libxext development package")
     endif()
+
+    list(APPEND glfw_LIBRARIES ${X11_X11_LIB})
 endif()
 
 #--------------------------------------------------------------------