diff --git a/languages/c/SpectralEntropy.c b/languages/c/SpectralEntropy.c
index f4f2453..a6005f6 100644
--- a/languages/c/SpectralEntropy.c
+++ b/languages/c/SpectralEntropy.c
@@ -57,7 +57,13 @@ float calculate_unweighted_entropy_similarity(
             b++;
         }
     }
-    return similarity / 2;
+    similarity = similarity / 2;
+    if (similarity < 0) {
+        similarity = 0;
+    }elif(similarity > 1) {
+        similarity = 1;
+    }
+    return similarity;
 }
 
 // Calculate entropy similarity
diff --git a/ms_entropy/spectra/entropy_cython.pyx b/ms_entropy/spectra/entropy_cython.pyx
index 8dc9cbd..08bb2d3 100644
--- a/ms_entropy/spectra/entropy_cython.pyx
+++ b/ms_entropy/spectra/entropy_cython.pyx
@@ -178,6 +178,8 @@ cpdef float cy_calculate_entropy_similarity(
     float
         The entropy similarity between the two spectra.
     """
+    if len(peaks_a) == 0 or len(peaks_b) == 0:
+        return 0.0
     cdef np.ndarray[float32, ndim=2] peaks_a_np = np.array(peaks_a, dtype=np.float32, copy=True, order="C")
     cdef np.ndarray[float32, ndim=2] peaks_b_np = np.array(peaks_b, dtype=np.float32, copy=True, order="C")
 
@@ -248,6 +250,8 @@ cpdef float cy_calculate_unweighted_entropy_similarity(
     float
         The unweighted entropy similarity between the two spectra.
     """
+    if len(peaks_a) == 0 or len(peaks_b) == 0:
+        return 0.0
     cdef np.ndarray[float32, ndim=2] peaks_a_np
     cdef np.ndarray[float32, ndim=2] peaks_b_np
     if clean_spectra:
diff --git a/ms_entropy/version.py b/ms_entropy/version.py
index e398332..07f744c 100644
--- a/ms_entropy/version.py
+++ b/ms_entropy/version.py
@@ -1 +1 @@
-__version__ = '1.3.2'
+__version__ = '1.3.3'