diff --git a/lectures/parallelism/slides.qmd b/lectures/parallelism/slides.qmd
index f695b35023df9441b6876ccedd51d6748274dae1..9616a12836037d0b71b9fc148abe11d1397ebaf1 100644
--- a/lectures/parallelism/slides.qmd
+++ b/lectures/parallelism/slides.qmd
@@ -126,12 +126,12 @@ module load gcc
 ```
 2. Compile and run the serial example
 ```bash
-gcc -O3 main.c -o serial.x -lm
+gcc main.c -o serial.x -lm
 time ./serial.x   # use `time` to check the runtime
 ```
 3. Compile and run the example using OpenMP
 ```bash
-gcc -O3 -fopenmp main.c -o parallel.x -lm
+gcc -fopenmp main.c -o parallel.x -lm
 export OMP_NUM_THREADS=2
 time ./parallel.x
 ```