diff --git a/libs/libc/include/stdio.h b/libs/libc/include/stdio.h
index 72755dda..853fd4df 100644
--- a/libs/libc/include/stdio.h
+++ b/libs/libc/include/stdio.h
@@ -98,6 +98,8 @@ extern "C"
     /* Retrieves a character from stream. */
     int getc(FILE* stream);
 
+    int ungetc(int, FILE*); // Not implemented.
+
     /* Retrieves a character from standard input. */
     int getchar();
 
diff --git a/libs/libc/src/file.cpp b/libs/libc/src/file.cpp
index 2ce93106..74507216 100644
--- a/libs/libc/src/file.cpp
+++ b/libs/libc/src/file.cpp
@@ -170,6 +170,11 @@ extern "C"
         return fgetc(stdin);
     }
 
+    int ungetc(int, FILE*)
+    {
+        NOT_IMPLEMENTED("ungetc");
+    }
+
     int ferror(FILE* stream)
     {
         return stream->f_err;