diff --git a/doc/CMakeLists.txt b/doc/CMakeLists.txt
index 3a1ac3a..d3872d2 100644
--- a/doc/CMakeLists.txt
+++ b/doc/CMakeLists.txt
@@ -3,6 +3,13 @@ cmake_minimum_required(VERSION 3.13)
 find_program(SCDOC_EXECUTABLE scdoc)
 find_program(GZIP_EXECUTABLE gzip)
 
+if (SCDOC_EXECUTABLE STREQUAL "SCDOC_EXECUTABLE-NOTFOUND")
+  message(FATAL_ERROR "scdoc not found; required to build man pages")
+endif ()
+if (GZIP_EXECUTABLE STREQUAL "GZIP_EXECUTABLE-NOTFOUND")
+  message(FATAL_ERROR "gzip not found; required to build man pages")
+endif ()
+
 function(add_man_pages)
   foreach (src ${ARGN})
     string(REPLACE ".scd" ".gz" man "${src}")