diff --git a/opm/core/pressure/msmfem/coarse_sys.c b/opm/core/pressure/msmfem/coarse_sys.c
index 3cae75c3..10337e8e 100644
--- a/opm/core/pressure/msmfem/coarse_sys.c
+++ b/opm/core/pressure/msmfem/coarse_sys.c
@@ -723,6 +723,8 @@ blkdof_fill(struct coarse_topology *ct,
 
     nb = ct->nblocks;
 
+    assert(nb > 0);
+
     sys->blkdof_pos = malloc((nb + 1) * sizeof *sys->blkdof_pos);
 
     if (sys->blkdof_pos != NULL) {
@@ -824,6 +826,8 @@ coarse_sys_allocate(struct coarse_topology *ct,
     if (new != NULL) {
         nb = ct->nblocks;
 
+        assert(nb > 0);
+
         alloc_ok = blkdof_fill(ct, m, new);
 
         if (alloc_ok) {
diff --git a/opm/core/pressure/msmfem/partition.c b/opm/core/pressure/msmfem/partition.c
index a056258f..a2eba629 100644
--- a/opm/core/pressure/msmfem/partition.c
+++ b/opm/core/pressure/msmfem/partition.c
@@ -138,6 +138,7 @@ partition_compress(int n, int *p)
     int ret, i, max, *compr;
 
     max = -1;
+    assert(n > 0);
     for (i = 0; i < n; i++) {
         assert (0 <= p[i]);     /* Only non-neg partitions (for now?). */
         max = MAX(max, p[i]);
@@ -313,6 +314,9 @@ partition_create_c2c(int nc, int nneigh, const int *neigh,
 {
     int i, ret, c1, c2;
 
+    assert(nc > 0);
+    assert(nneigh > 0);
+
     *pc2c = malloc((nc + 1) * sizeof **pc2c);
 
     if (*pc2c != NULL) {
diff --git a/opm/core/utility/writeVtkData.cpp b/opm/core/utility/writeVtkData.cpp
index 262ec35d..07e57172 100644
--- a/opm/core/utility/writeVtkData.cpp
+++ b/opm/core/utility/writeVtkData.cpp
@@ -44,7 +44,7 @@ namespace Opm
 	int num_cells = dims[0]*dims[1]*dims[2];
 
 	ASSERT(dimension == 2 || dimension == 3);
-	ASSERT(num_cells = dims[0]*dims[1]* (dimension == 2 ? 1 : dims[2]));
+	ASSERT(num_cells == dims[0]*dims[1]* (dimension == 2 ? 1 : dims[2]));
 
 	os << "# vtk DataFile Version 2.0\n";
 	os << "Structured Grid\n \n";