diff --git a/vaporetto/src/char_scorer.rs b/vaporetto/src/char_scorer.rs
index 41d00b8c..8e9cf1b3 100644
--- a/vaporetto/src/char_scorer.rs
+++ b/vaporetto/src/char_scorer.rs
@@ -92,6 +92,12 @@ impl CharScorer {
         window_size: u8,
         #[cfg(feature = "tag-prediction")] tag_ngram_model: Vec<TagNgramModel<String>>,
     ) -> Result<Self> {
+        if window_size == 0 {
+            return Err(Vaporetto::invalid_model(
+                "char_window_size must be a positive value",
+            ));
+        }
+
         #[cfg(feature = "tag-prediction")]
         if tag_ngram_model.is_empty() {
             Ok(Self::Boundary(CharScorerBoundary::new(
diff --git a/vaporetto/src/type_scorer.rs b/vaporetto/src/type_scorer.rs
index c7eff84a..f613ab28 100644
--- a/vaporetto/src/type_scorer.rs
+++ b/vaporetto/src/type_scorer.rs
@@ -14,7 +14,7 @@ use alloc::vec::Vec;
 
 use bincode::{BorrowDecode, Encode};
 
-use crate::errors::Result;
+use crate::errors::{Result, VaporettoError};
 use crate::ngram_model::NgramModel;
 use crate::sentence::Sentence;
 
@@ -105,11 +105,16 @@ impl TypeScorer {
         #[cfg(feature = "tag-prediction")]
         if tag_ngram_model.is_empty() {
             match window_size {
+                0 => Err(Vaporetto::invalid_model(
+                    "type_window_size must be a positive value",
+                )),
+
                 #[cfg(feature = "cache-type-score")]
-                0..=CACHE_MAX_WINDOW_SIZE => Ok(Self::BoundaryCache(TypeScorerBoundaryCache::new(
+                1..=CACHE_MAX_WINDOW_SIZE => Ok(Self::BoundaryCache(TypeScorerBoundaryCache::new(
                     ngram_model,
                     window_size,
                 )?)),
+
                 _ => Ok(Self::Boundary(TypeScorerBoundary::new(
                     ngram_model,
                     window_size,