diff --git a/Dockerfile.custom b/Dockerfile.custom
index 993d265..75ba319 100644
--- a/Dockerfile.custom
+++ b/Dockerfile.custom
@@ -10,19 +10,21 @@ WORKDIR /app
 COPY Cargo.toml .
 COPY src ./src
 
-RUN mkdir -p /root/.cargo && printf '\
-    [profile.release]\n\
-    lto = true\n\
-    codegen-units = 1\n\
-    opt-level = '3'\n\
-    panic = "abort"\n\
-    strip = true\n
-    [target.x86_64-unknown-linux-gnu]\n\
-    rustflags = [\n\
-        "-C", "target-cpu=native",\n\
-        "-C", "codegen-units=1",\n\
-        "-C", "debuginfo=0"\n\
-    ]\n' > /root/.cargo/config.toml
+RUN mkdir -p /root/.cargo && cat > /root/.cargo/config.toml <<'EOF'
+[profile.release]
+lto = true
+codegen-units = 1
+opt-level = '3'
+panic = "abort"
+strip = true
+
+[target.x86_64-unknown-linux-gnu]
+rustflags = [
+    "-C", "target-cpu=native",
+    "-C", "codegen-units=1",
+    "-C", "debuginfo=0"
+]
+EOF
 
 RUN curl https://sh.rustup.rs -sSf | sh -s -- -y