diff --git a/CMakeLists.txt b/CMakeLists.txt
index e925a0b8df..afbc837828 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -788,7 +788,13 @@ set (_ALL_SOURCE 1)
 set (_GNU_SOURCE 1)
 set (_POSIX_PTHREAD_SEMANTICS 1)
 set (_TANDEM_SOURCE 1)
-set (__EXTENSIONS__ 1)
+endif()
+
+# Solaris header files limit the visibility of non-standard extensions
+# unless __EXTENSIONS__ is defined.  We need some of those
+# non-standard interfaces.
+if (CMAKE_SYSTEM_NAME MATCHES "SunOS")
+add_compile_definitions(__EXTENSIONS__=1)
 endif()
 
 check_struct_has_member("struct tm" tm_gmtoff time.h have_struct_tm_gmtoff)
diff --git a/common/config.h.cmake.in b/common/config.h.cmake.in
index 77d555ccfa..e1ed479509 100644
--- a/common/config.h.cmake.in
+++ b/common/config.h.cmake.in
@@ -290,11 +290,6 @@
 #ifndef _TANDEM_SOURCE
 #cmakedefine _TANDEM_SOURCE 1
 #endif
-/* Enable general extensions on Solaris.  */
-#ifndef __EXTENSIONS__
-#cmakedefine __EXTENSIONS__ 1
-#endif
-
 
 /* Define WORDS_BIGENDIAN to 1 if your processor stores words with the most
    significant byte first (like Motorola and SPARC, unlike Intel). */
diff --git a/libgnucash/backend/xml/sixtp-dom-generators.cpp b/libgnucash/backend/xml/sixtp-dom-generators.cpp
index a949b65a52..98cba3bfeb 100644
--- a/libgnucash/backend/xml/sixtp-dom-generators.cpp
+++ b/libgnucash/backend/xml/sixtp-dom-generators.cpp
@@ -21,9 +21,6 @@
  *                                                                  *
  ********************************************************************/
 #include <glib.h>
-
-#define __EXTENSIONS__
-
 #include <config.h>
 
 #include <gnc-date.h>
diff --git a/libgnucash/backend/xml/sixtp-utils.cpp b/libgnucash/backend/xml/sixtp-utils.cpp
index 4e3539ad3c..575ae60f24 100644
--- a/libgnucash/backend/xml/sixtp-utils.cpp
+++ b/libgnucash/backend/xml/sixtp-utils.cpp
@@ -21,7 +21,6 @@
  *                                                                  *
  ********************************************************************/
 
-#define __EXTENSIONS__
 #include <guid.hpp>
 #include <config.h>
 
diff --git a/libgnucash/engine/gnc-date.cpp b/libgnucash/engine/gnc-date.cpp
index f64863888d..2302ae6295 100644
--- a/libgnucash/engine/gnc-date.cpp
+++ b/libgnucash/engine/gnc-date.cpp
@@ -25,7 +25,6 @@
  *                                                                  *
 \********************************************************************/
 
-#define __EXTENSIONS__
 #include <glib.h>
 
 #include <config.h>