diff --git a/src/mcx_utils.c b/src/mcx_utils.c
index 0b20d56e..92a46c38 100644
--- a/src/mcx_utils.c
+++ b/src/mcx_utils.c
@@ -331,7 +331,7 @@ void mcx_initcfg(Config* cfg) {
     cfg->nphase = 0;
     cfg->invcdf = NULL;
     memset(cfg->jsonfile, 0, MAX_PATH_LENGTH);
-    memset(cfg->bc, 0, 12);
+    memset(cfg->bc, 0, 13);
     memset(&(cfg->srcparam1), 0, sizeof(float4));
     memset(&(cfg->srcparam2), 0, sizeof(float4));
     memset(cfg->deviceid, 0, MAX_DEVICE);
diff --git a/src/mcx_utils.h b/src/mcx_utils.h
index ddcf44f4..dcd24e95 100644
--- a/src/mcx_utils.h
+++ b/src/mcx_utils.h
@@ -258,7 +258,7 @@ typedef struct MCXConfig {
     float* dx;                   /**< anisotropic voxel spacing for x-axis */
     float* dy;                   /**< anisotropic voxel spacing for y-axis */
     float* dz;                   /**< anisotropic voxel spacing for z-axis */
-    char bc[12];                 /**<boundary condition flag for [-x,-y,-z,+x,+y,+z, det(-x,-y,-z,+x,+y,+z)] */
+    char bc[13];                 /**<boundary condition flag for [-x,-y,-z,+x,+y,+z, det(-x,-y,-z,+x,+y,+z)] */
     unsigned int nphase;         /**< number of samples for inverse-cdf, will be added by 2 to include -1 and 1 on the two ends */
     float* invcdf;               /**< equal-space sampled inversion of CDF(cos(theta)) for the phase function of the zenith angle */
 } Config;