diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index ccc3d132..c090fef7 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -348,10 +348,6 @@ endif (WITH_SYMBOL_VERSIONING AND HAVE_LD_VERSION_SCRIPT AND ABIMAP_FOUND)
 # This gets built as a static library, if -DBUILD_SHARED_LIBS=OFF is passed to
 # cmake.
 add_library(ssh ${libssh_SRCS})
-target_compile_options(ssh
-                       PRIVATE
-                           ${DEFAULT_C_COMPILE_FLAGS}
-                           -D_GNU_SOURCE)
 target_include_directories(ssh
                            PUBLIC
                                $<BUILD_INTERFACE:${libssh_SOURCE_DIR}/include>
@@ -408,10 +404,6 @@ install(EXPORT libssh-config
 
 if (BUILD_STATIC_LIB)
   add_library(ssh-static STATIC ${libssh_SRCS})
-  target_compile_options(ssh-static
-                         PRIVATE
-                            ${DEFAULT_C_COMPILE_FLAGS}
-                            -D_GNU_SOURCE)
 
   target_include_directories(ssh-static
                              PUBLIC
diff --git a/src/misc.c b/src/misc.c
index 11a7479c..1de53fcd 100644
--- a/src/misc.c
+++ b/src/misc.c
@@ -1956,7 +1956,7 @@ char *ssh_strerror(int err_num, char *buf, size_t buflen)
 #if defined(_WIN32)
     strerror_s(buf, buflen, err_num);
     return buf;
-#elif defined(__linux__) && defined(_GNU_SOURCE)
+#elif defined(__linux__) && defined(__GLIBC__) && defined(_GNU_SOURCE)
     /* GNU extension on Linux */
     return strerror_r(err_num, buf, buflen);
 #else
diff --git a/tests/torture.h b/tests/torture.h
index fa215713..58feb21e 100644
--- a/tests/torture.h
+++ b/tests/torture.h
@@ -24,10 +24,6 @@
 #ifndef _TORTURE_H
 #define _TORTURE_H
 
-#ifndef _GNU_SOURCE
-#define _GNU_SOURCE
-#endif
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdarg.h>