diff --git a/dlib/matrix/matrix_utilities.h b/dlib/matrix/matrix_utilities.h
index ffa922c3b..caec2707d 100644
--- a/dlib/matrix/matrix_utilities.h
+++ b/dlib/matrix/matrix_utilities.h
@@ -171,6 +171,11 @@ namespace dlib
         const matrix_exp<EXP>& m
     )
     {
+        DLIB_ASSERT(m.size() > 0, 
+            "\ttype max(const matrix_exp& m)"
+            << "\n\tYou can't ask for the max() of an empty matrix"
+            << "\n\tm.size():     " << m.size() 
+            );
         typedef typename matrix_exp<EXP>::type type;
 
         type val = m(0,0);
@@ -195,6 +200,11 @@ namespace dlib
         const matrix_exp<EXP>& m
     )
     {
+        DLIB_ASSERT(m.size() > 0, 
+            "\ttype min(const matrix_exp& m)"
+            << "\n\tYou can't ask for the min() of an empty matrix"
+            << "\n\tm.size():     " << m.size() 
+            );
         typedef typename matrix_exp<EXP>::type type;
 
         type val = m(0,0);
diff --git a/dlib/matrix/matrix_utilities_abstract.h b/dlib/matrix/matrix_utilities_abstract.h
index 2763a7c9c..e9e1f80af 100644
--- a/dlib/matrix/matrix_utilities_abstract.h
+++ b/dlib/matrix/matrix_utilities_abstract.h
@@ -682,6 +682,8 @@ namespace dlib
         const matrix_exp& m
     );
     /*!
+        requires
+            - m.size() > 0
         ensures
             - returns the value of the smallest element of m
     !*/
@@ -692,6 +694,8 @@ namespace dlib
         const matrix_exp& m
     );
     /*!
+        requires
+            - m.size() > 0
         ensures
             - returns the value of the biggest element of m
     !*/