diff --git a/src/kbmod/search/psf.cpp b/src/kbmod/search/psf.cpp
index fa2735cbb..ee25f75a3 100644
--- a/src/kbmod/search/psf.cpp
+++ b/src/kbmod/search/psf.cpp
@@ -87,7 +87,12 @@ PSF& PSF::operator=(PSF&& other) {
 
 void PSF::calc_sum() {
     sum = 0.0;
-    for (auto& i : kernel) sum += i;
+    for (auto& i : kernel) {
+        if (std::isnan(i) || std::isinf(i)) {
+            throw std::runtime_error("Invalid value in PSF kernel (NaN or inf)");
+        }
+        sum += i;
+    }
 }
 
 void PSF::square_psf() {
diff --git a/src/kbmod/search/psf.h b/src/kbmod/search/psf.h
index 37b7a4d26..2dc96a17b 100644
--- a/src/kbmod/search/psf.h
+++ b/src/kbmod/search/psf.h
@@ -31,18 +31,20 @@ class PSF {
     float get_std() const { return width; }
     float get_sum() const { return sum; }
     float get_value(int x, int y) const { return kernel[y * dim + x]; }
-    int get_dim() const { return dim; }
+    int get_dim() const { return dim; }  // Length of one side of the kernel.
     int get_radius() const { return radius; }
     int get_size() const { return kernel.size(); }
     const std::vector<float>& get_kernel() const { return kernel; };
     float* data() { return kernel.data(); }
 
     // Computation functions.
-    void calc_sum();
     void square_psf();
     std::string print();
 
 private:
+    // Validates the PSF array and computes the sum.
+    void calc_sum();
+
     std::vector<float> kernel;
     float width;
     float sum;
diff --git a/src/kbmod/search/pydocs/psf_docs.h b/src/kbmod/search/pydocs/psf_docs.h
index a58fb07f4..22e18cabd 100644
--- a/src/kbmod/search/pydocs/psf_docs.h
+++ b/src/kbmod/search/pydocs/psf_docs.h
@@ -23,7 +23,8 @@ static const auto DOC_PSF = R"doc(
 
   Raises
   ------
-  Raises a ``RuntimeError`` when given an invalid stdev.
+  Raises a ``RuntimeError`` when given an invalid stdev or an array
+  containing invalid entries, such as NaN or infinity.
   )doc";
 
 static const auto DOC_PSF_set_array = R"doc(
@@ -49,11 +50,11 @@ static const auto DOC_PSF_get_sum = R"doc(
   ")doc";
 
 static const auto DOC_PSF_get_dim = R"doc(
-  "Returns the PSF kernel dimensions.
+  "Returns the PSF kernel dimension D where the kernel is a D by D array.
   ")doc";
 
 static const auto DOC_PSF_get_radius = R"doc(
-  "Returns the radius of the PSF
+  "Returns the radius of the PSF.
   ")doc";
 
 static const auto DOC_PSF_get_size = R"doc(
diff --git a/tests/test_psf.py b/tests/test_psf.py
index a7eba0ea9..bb37d9157 100644
--- a/tests/test_psf.py
+++ b/tests/test_psf.py
@@ -1,3 +1,5 @@
+import math
+import numpy as np
 import unittest
 
 from kbmod.search import PSF
@@ -19,10 +21,24 @@ def test_make_noop(self):
         self.assertEqual(len(kernel0), 1)
         self.assertEqual(kernel0[0], 1.0)
 
-    def test_make_invalud(self):
+    def test_make_invalid(self):
         # Raise an error if creating a PSF with a negative stdev.
         self.assertRaises(RuntimeError, PSF, -1.0)
 
+    def test_make_from_array(self):
+        arr = np.full((3, 3), 1.0 / 9.0)
+        psf_arr = PSF(arr)
+        self.assertEqual(psf_arr.get_size(), 9)
+        self.assertEqual(psf_arr.get_dim(), 3)
+
+        # We get an error if we include a NaN.
+        arr[0][0] = math.nan
+        self.assertRaises(RuntimeError, PSF, arr)
+
+        # We get an error if we include a inf.
+        arr[0][0] = math.inf
+        self.assertRaises(RuntimeError, PSF, arr)
+
     def test_to_string(self):
         result = self.psf_list[0].__str__()
         self.assertGreater(len(result), 1)