diff --git a/src/core.cpp b/src/core.cpp
index 23cc87aa..a4fc57aa 100644
--- a/src/core.cpp
+++ b/src/core.cpp
@@ -117,7 +117,7 @@ void Core::step() {
   if (USE_DEBUG >= 3) {
     D(3, "Register state:");
     for (unsigned i = 0; i < reg[0].size(); ++i) {
-      D_RAW(dec << "  %r" << i << ':');
+      D_RAW("  %r" << dec << i << ':');
       for (unsigned j = 0; j < reg.size(); ++j) 
         D_RAW(' ' << hex << reg[j][i] << ' ');
       D_RAW('(' << shadowReg[i] << ')' << endl);
diff --git a/src/instruction.cpp b/src/instruction.cpp
index aaddb5d4..6b551c1a 100644
--- a/src/instruction.cpp
+++ b/src/instruction.cpp
@@ -87,17 +87,17 @@ ostream &Harp::operator<<(ostream& os, Instruction &inst) {
   os << dec;
 
   if (inst.predicated) {
-    os << "@p" << inst.pred << " ? ";
+    os << "@p" << dec << inst.pred << " ? ";
   }
 
   os << Instruction::instTable[inst.op].opString << ' ';
-  if (inst.rdestPresent) os << "%r" << inst.rdest << ' ';
+  if (inst.rdestPresent) os << "%r" << dec << inst.rdest << ' ';
   if (inst.pdestPresent) os << "@p" << inst.pdest << ' ';
   for (int i = 0; i < inst.nRsrc; i++) {
-    os << "%r" << inst.rsrc[i] << ' ';
+    os << "%r" << dec << inst.rsrc[i] << ' ';
   }
   for (int i = 0; i < inst.nPsrc; i++) {
-    os << "@p" << inst.psrc[i] << ' ';
+    os << "@p" << dec << inst.psrc[i] << ' ';
   }
   if (inst.immsrcPresent) {
     if (inst.refLiteral) os << inst.refLiteral->name;
@@ -290,4 +290,9 @@ void Instruction::executeOn(Core &c) {
   D(3, "End instruction execute.");
 
   c.activeThreads = nextActiveThreads;
+  if (nextActiveThreads > c.reg.size()) {
+    cerr << "Error: attempt to spawn " << nextActiveThreads << " threads. "
+         << c.reg.size() << " available.\n";
+    abort();
+  }
 }
diff --git a/src/test/matmul-mt.s b/src/test/matmul-mt.s
index c8c76bd3..83f550ff 100644
--- a/src/test/matmul-mt.s
+++ b/src/test/matmul-mt.s
@@ -12,7 +12,8 @@
 .perm x
 .entry
 .global
-entry: ldi %r0, matrix_a;
+entry:
+       ldi %r0, matrix_a;
        ldi %r1, #3;
        jali %r5, matgen;
 
@@ -98,14 +99,15 @@ sloop:  add %r0, %r0, %r17;
  */
 matmulthd: ldi %r9, #0; /* result row: %r9 */
 rloop:     ldi %r6, #0; /* result col: %r6 */
+
 cloop:     shli %r16, %r6, (`__WORD);
            shl %r15, %r9, %r10;
 
            add %r11, %r15, %r0;
            add %r12, %r16, %r1;
-           ldi %r13, #0;
 
            ldi %r8, #0 /* dot prod position: %r8 */
+           ldi %r13, #0;
 iloop:     ld %r7, %r11, #0;
            ld %r23, %r12, #0;
            fmul %r7, %r7, %r23
@@ -129,6 +131,7 @@ iloop:     ld %r7, %r11, #0;
 
            addi %r9, %r9, #1;
            sub %r7, %r9, %r24;
+
            rtop @p0, %r7;
      @p0 ? jmpi rloop;