diff --git a/tools/testing/selftests/powerpc/ptrace/core-pkey.c b/tools/testing/selftests/powerpc/ptrace/core-pkey.c
index 1a70a96f0bfe7251d6b4e3a568985401a09b0770..4e8d0ce1ff58f79ee0136aa3a7fb11bc9c049324 100644
--- a/tools/testing/selftests/powerpc/ptrace/core-pkey.c
+++ b/tools/testing/selftests/powerpc/ptrace/core-pkey.c
@@ -383,7 +383,7 @@ static int setup_core_pattern(char **core_pattern_, bool *changed_)
 		goto out;
 	}
 
-	ret = fread(core_pattern, 1, PATH_MAX, f);
+	ret = fread(core_pattern, 1, PATH_MAX - 1, f);
 	fclose(f);
 	if (!ret) {
 		perror("Error reading core_pattern file");
@@ -391,6 +391,8 @@ static int setup_core_pattern(char **core_pattern_, bool *changed_)
 		goto out;
 	}
 
+	core_pattern[ret] = '\0';
+
 	/* Check whether we can predict the name of the core file. */
 	if (!strcmp(core_pattern, "core") || !strcmp(core_pattern, "core.%p"))
 		*changed_ = false;