diff --git a/c_runtime/matrix.h b/c_runtime/matrix.h
index 7c4145732ee..681e4e4e909 100644
--- a/c_runtime/matrix.h
+++ b/c_runtime/matrix.h
@@ -28,10 +28,12 @@ void hybrd_(void (*) (int*, double *, double*, int*),
 #endif
 
 #define declare_matrix(A,nrows,ncols) double *A = new double[nrows*ncols]; \
-assert(A!=0); 
+assert(A!=0); \
+for (int i=0;i<nrows*ncols;i++) A[i]=0.0;
 
 #define declare_vector(v,nelts) double *v=new double[nelts];\
-assert(v!=0);
+assert(v!=0); \
+for (int i=0;i<nelts;i++) v[i]=0.0;
 
 /* Matrixes using column major order (as in Fortran) */
 #define set_matrix_elt(A,r,c,n_rows,value) A[r+n_rows*c]=value