diff --git a/ebwt_build.cpp b/ebwt_build.cpp
index c47603d..1cf3241 100644
--- a/ebwt_build.cpp
+++ b/ebwt_build.cpp
@@ -216,6 +216,7 @@ static int parseNumber(T lower, const char *errmsg) {
 static void parseOptions(int argc, const char **argv) {
 	int option_index = 0;
 	int next_option;
+	bool bmaxDivNSet = false;
 	do {
 		next_option = getopt_long(
 			argc, const_cast<char**>(argv),
@@ -261,6 +262,7 @@ static void parseOptions(int argc, const char **argv) {
 				bmaxDivN = 0xffffffff; // don't use multSqrt
 				break;
 			case ARG_BMAX_DIV:
+				bmaxDivNSet = true;
 				bmaxDivN = parseNumber<uint32_t>(1, "--bmaxdivn arg must be at least 1");
 				bmax = OFF_MASK;         // don't use bmax
 				bmaxMultSqrt = OFF_MASK; // don't use multSqrt
@@ -296,6 +298,9 @@ static void parseOptions(int argc, const char **argv) {
 		     << "extremely slow performance and memory exhaustion.  Perhaps you meant to specify" << endl
 		     << "a small --bmaxdivn?" << endl;
 	}
+	if (!bmaxDivNSet) {
+		bmaxDivN *= nthreads;
+	}
 }
 
 /**