diff --git a/dlib/matrix/matrix_subexp.h b/dlib/matrix/matrix_subexp.h
index 3f246dcd2..0b68ee772 100644
--- a/dlib/matrix/matrix_subexp.h
+++ b/dlib/matrix/matrix_subexp.h
@@ -235,7 +235,7 @@ namespace dlib
     )
     {
         DLIB_ASSERT(row >= 0 && row < m.nr() && 
-                    length >= 0 && length < m.nc(), 
+                    length >= 0 && length <= m.nc(), 
             "\tconst matrix_exp rowm(const matrix_exp& m, row, length)"
             << "\n\tYou have specified invalid sub matrix dimensions"
             << "\n\tm.nr(): " << m.nr()
@@ -375,7 +375,7 @@ namespace dlib
     )
     {
         DLIB_ASSERT(col >= 0 && col < m.nc() && 
-                    length >= 0 && length < m.nr(), 
+                    length >= 0 && length <= m.nr(), 
             "\tconst matrix_exp colm(const matrix_exp& m, col, length)"
             << "\n\tYou have specified invalid sub matrix dimensions"
             << "\n\tm.nr(): " << m.nr()
diff --git a/dlib/matrix/matrix_subexp_abstract.h b/dlib/matrix/matrix_subexp_abstract.h
index dfb253126..f86f6c334 100644
--- a/dlib/matrix/matrix_subexp_abstract.h
+++ b/dlib/matrix/matrix_subexp_abstract.h
@@ -160,7 +160,7 @@ namespace dlib
     /*!
         requires
             - 0 <= row < m.nr()
-            - 0 <= length < m.nc()
+            - 0 <= length <= m.nc()
         ensures
             - returns a matrix R such that:
                 - R.nr() == 1
@@ -198,7 +198,7 @@ namespace dlib
     );
     /*!
         requires
-            - 0 <= col < m.nr()
+            - 0 <= col < m.nc()
         ensures
             - returns a matrix R such that:
                 - R.nr() == m.nr() 
@@ -216,8 +216,8 @@ namespace dlib
     );
     /*!
         requires
-            - 0 <= col < m.nr()
-            - 0 <= length < m.nc()
+            - 0 <= col < m.nc()
+            - 0 <= length <= m.nr()
         ensures
             - returns a matrix R such that:
                 - R.nr() == length