diff --git a/Cargo.toml b/Cargo.toml
index 39881443561..d0f6a7e2449 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -51,6 +51,10 @@ serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0.61"
 rayon = "1.0.2"
 widestring = "0.5.1"
+# plotters via criterion, 0.3.2 requires edition: 2021 (Rust 1.56)
+plotters = { version = "=0.3.1", default-features = false }
+plotters-backend = { version = "=0.3.2", default-features = false }
+plotters-svg = { version = "=0.3.1", default-features = false }
 
 [build-dependencies]
 pyo3-build-config = { path = "pyo3-build-config", version = "0.16.5", features = ["resolve-config"] }