diff --git a/c-programming/reverse-ramdisk.c b/c-programming/reverse-ramdisk.c
index 1300d45..f44280b 100644
--- a/c-programming/reverse-ramdisk.c
+++ b/c-programming/reverse-ramdisk.c
@@ -5,7 +5,6 @@ C programming idea: Handling temporary files like memory allocations (allocating
 
 Warning: The current result is quick and dirty. Not for educational or
 production purposes.
-Warning: The functions are not thread-safe.
 
 GCC/Clang/TCC: Compile with -DTEST to set macro TEST as defined, with -DDEBUG
 to enable debug mode
@@ -16,6 +15,7 @@ To-Do: Add thread-safe versions of functions (use postfix `_r`)
 #include <errno.h>
 #include <inttypes.h>
 #include <math.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -40,6 +40,7 @@ To-Do: Add thread-safe versions of functions (use postfix `_r`)
 } while (0)
 
 typedef struct {
+	bool locked;
 	int ID;
 	char* file_path;
 #if IS_POSIX
@@ -96,6 +97,7 @@ int tf_alloc(size_t n, size_t type_size) {
 	}
 
 	// Assign the ID, file path, file handler
+	temp_file->locked = false;
 	temp_file->ID = num_temp_files;
 	temp_file->file_path = strdup(file_path);
 	temp_file->file = file;
@@ -120,6 +122,12 @@ int tf_alloc(size_t n, size_t type_size) {
 int tf_free(int ID) {
 	size_t index = (size_t) ID;
 
+	if (temp_files[index].locked) {
+		errno = EBUSY;
+		return -1;
+	}
+	temp_files[index].locked = true;
+
 #if IS_POSIX
 	close(temp_files[index].file);
 #else
@@ -147,12 +155,20 @@ int tf_free(int ID) {
 		return -1;
 	}
 
+	temp_files[index].locked = false;
+
 	return 0;
 }
 
 int tf_write(int ID, size_t offset, void* src, size_t data_size) {
 	size_t index = (size_t) ID;
 
+	if (temp_files[index].locked) {
+		errno = EBUSY;
+		return -1;
+	}
+	temp_files[index].locked = true;
+
 #if IS_POSIX
 	// Check file handler for -1
 	int file = temp_files[index].file;
@@ -199,12 +215,20 @@ int tf_write(int ID, size_t offset, void* src, size_t data_size) {
 	fflush(file);
 #endif
 
+	temp_files[index].locked = false;
+
 	return 0;
 }
 
 int tf_read(int ID, size_t offset, void* dest, size_t data_size) {
 	size_t index = (size_t) ID;
 
+	if (temp_files[index].locked) {
+		errno = EBUSY;
+		return -1;
+	}
+	temp_files[index].locked = true;
+
 #if IS_POSIX
 	int file = temp_files[index].file;
 	if (file == -1)
@@ -264,6 +288,9 @@ int tf_read(int ID, size_t offset, void* dest, size_t data_size) {
 	printf("'\n");
 	fflush(stdout);
 #endif
+
+	temp_files[index].locked = false;
+
 	return 0;
 }