diff --git a/Dockerfile b/Dockerfile
index d330367..3956dd1 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -52,13 +52,14 @@ RUN sed -i 's/-zx/-ozx/g' \
   /usr/class/assignments/PA4J/grade.pl /usr/class/assignments/PA4/grade.pl \
   /usr/class/assignments/PA5J/grade.pl /usr/class/assignments/PA5/grade.pl
 
-# Patch cool.flex in submission folder
+# Patch cool.flex, cool.y in submission folder
 # This is a hack to
 #   a) satisfy the cool compiler which expects yylex to be named cool_yylex
 #   b) satisfy libfl > 2.5.39 which expects a yylex symbol
 #   c) fix mangling errors of yylex when compiled with a c++ compiler
 #   d) be as non-invasive as possible to the existing assignment code
-RUN patch -u /usr/class/assignments/PA2/cool.flex -i /tmp/build/cool.flex.patch
+RUN patch -u /usr/class/assignments/PA2/cool.flex -i /tmp/build/cool.flex.patch \
+    && patch -u /usr/class/assignments/PA3/cool.y -i /tmp/build/cool.y.patch
 
 # Setup working directory
 RUN mkdir -p /class
diff --git a/cool.y.patch b/cool.y.patch
new file mode 100644
index 0000000..c31e145
--- /dev/null
+++ b/cool.y.patch
@@ -0,0 +1,26 @@
+--- cool.y	2020-12-22 01:57:18.912461835 +0000
++++ cool.y.work	2020-12-22 01:57:06.089590582 +0000
+@@ -11,6 +11,23 @@
+   
+   extern char *curr_filename;
+   
++  /* This is a hack to
++   * a) satisfy the cool compiler which expects yylex to be named cool_yylex (see below)
++   * b) satisfy libfl > 2.5.39 which expects a yylex symbol
++   * c) fix mangling errors of yylex when compiled with a c++ compiler
++   * d) be as non-invasive as possible to the existing assignment code
++   *
++   * WARNING: We are now leaving standard country, but `push_macro` is supported
++   *          in all major compilers.
++   */
++  #pragma push_macro("yylex")
++  #undef yylex
++  int cool_yylex();
++  extern "C" {
++    int (&yylex) (void) = cool_yylex;
++  }
++  #pragma pop_macro("yylex")
++
+   
+   /* Locations */
+   #define YYLTYPE int              /* the type of locations */