diff --git a/repos/libports/src/lib/libc/file_operations.cc b/repos/libports/src/lib/libc/file_operations.cc
index e892dab551..6e61039f91 100644
--- a/repos/libports/src/lib/libc/file_operations.cc
+++ b/repos/libports/src/lib/libc/file_operations.cc
@@ -413,9 +413,15 @@ __SYS_(void *, mmap, (void *addr, ::size_t length,
                       int prot, int flags,
                       int libc_fd, ::off_t offset),
 {
-
 	/* handle requests for anonymous memory */
-	if (!addr && libc_fd == -1) {
+	if ((flags & MAP_ANONYMOUS) || (flags & MAP_ANON)) {
+
+		if (flags & MAP_FIXED) {
+			Genode::error("mmap for fixed predefined address not supported yet");
+			errno = EINVAL;
+			return MAP_FAILED;
+		}
+
 		bool const executable = prot & PROT_EXEC;
 		void *start = mem_alloc(executable)->alloc(length, PAGE_SHIFT);
 		if (!start) {
diff --git a/repos/libports/src/lib/libc/vfs_plugin.cc b/repos/libports/src/lib/libc/vfs_plugin.cc
index 02d193efbb..fef94b38bb 100644
--- a/repos/libports/src/lib/libc/vfs_plugin.cc
+++ b/repos/libports/src/lib/libc/vfs_plugin.cc
@@ -1640,8 +1640,8 @@ void *Libc::Vfs_plugin::mmap(void *addr_in, ::size_t length, int prot, int flags
 		return (void *)-1;
 	}
 
-	if (addr_in != 0) {
-		error("mmap for predefined address not supported");
+	if (flags & MAP_FIXED) {
+		error("mmap for fixed predefined address not supported yet");
 		errno = EINVAL;
 		return (void *)-1;
 	}