diff --git a/gen/instruction.go b/gen/instruction.go
new file mode 100644
index 0000000..24aecca
--- /dev/null
+++ b/gen/instruction.go
@@ -0,0 +1,15 @@
+package gen
+
+import "github.com/firestuff/subcoding/vm"
+
+func randInstruction() *vm.Instruction {
+	instr := &vm.Instruction{
+		OpCode: randOpCode(),
+	}
+
+	for i, t := range vm.OperandsByOpCode[instr.OpCode] {
+		instr.Operands[i] = randOperand(t)
+	}
+
+	return instr
+}
diff --git a/gen/opcode.go b/gen/opcode.go
new file mode 100644
index 0000000..5f69977
--- /dev/null
+++ b/gen/opcode.go
@@ -0,0 +1,52 @@
+package gen
+
+import "math/rand"
+
+import "github.com/firestuff/subcoding/vm"
+
+var opCodes = []vm.OpCodeType{
+	vm.OpNop,
+
+	vm.OpMov,
+
+	vm.OpAdd,
+	vm.OpSub,
+	vm.OpMul,
+	vm.OpDivU,
+	vm.OpDivS,
+
+	vm.OpNot,
+	vm.OpAnd,
+	vm.OpOr,
+	vm.OpXor,
+
+	vm.OpShR,
+	vm.OpShL,
+
+	vm.OpEq,
+	vm.OpLTU,
+	vm.OpLTS,
+	vm.OpGTU,
+	vm.OpGTS,
+	vm.OpLTEU,
+	vm.OpLTES,
+	vm.OpGTEU,
+	vm.OpGTES,
+
+	vm.OpJmp,
+	vm.OpJmpT,
+	vm.OpJmpF,
+
+	vm.OpCal,
+	vm.OpCalT,
+	vm.OpCalF,
+
+	vm.OpRet,
+	vm.OpRetT,
+	vm.OpRetF,
+}
+
+func randOpCode() vm.OpCodeType {
+	// Uniform distribution
+	return opCodes[rand.Intn(len(opCodes))]
+}
diff --git a/gen/operand.go b/gen/operand.go
new file mode 100644
index 0000000..0fc659b
--- /dev/null
+++ b/gen/operand.go
@@ -0,0 +1,50 @@
+package gen
+
+import "math/rand"
+
+import "github.com/firestuff/subcoding/vm"
+
+func randOperand(t vm.OperandNumericType) *vm.Operand {
+	for {
+		op := &vm.Operand{
+			Type: randOperandType(),
+		}
+
+		switch op.Type {
+		case vm.GlobalMemoryIndex:
+			op.Value = RandBiasedUint64()
+
+		case vm.FunctionMemoryIndex:
+			op.Value = RandBiasedUint64()
+
+		case vm.Literal:
+			switch t {
+			case vm.OperandUnsigned:
+				op.Value = RandBiasedUint64()
+
+			case vm.OperandSigned:
+				op.Value = RandBiasedInt64()
+
+			case vm.OperandSignedOrUnsigned:
+				op.Value = RandBiasedUSint64()
+
+			case vm.OperandReference:
+				// Invalid. Roll the dice again.
+				continue
+			}
+		}
+
+		return op
+	}
+}
+
+var operandTypes = []vm.OperandType{
+	vm.Literal,
+	vm.FunctionMemoryIndex,
+	vm.GlobalMemoryIndex,
+}
+
+func randOperandType() vm.OperandType {
+	// Uniform distribution
+	return operandTypes[rand.Intn(len(operandTypes))]
+}
diff --git a/gen/program.go b/gen/program.go
new file mode 100644
index 0000000..901c012
--- /dev/null
+++ b/gen/program.go
@@ -0,0 +1,15 @@
+package gen
+
+import "github.com/firestuff/subcoding/vm"
+
+func RandProgram() *vm.Program {
+	return &vm.Program{
+		Functions: []*vm.Function{
+			&vm.Function{
+				Instructions: []*vm.Instruction{
+					randInstruction(),
+				},
+			},
+		},
+	}
+}
diff --git a/gen/rand.go b/gen/rand.go
index ca1bcbd..021ee65 100644
--- a/gen/rand.go
+++ b/gen/rand.go
@@ -11,14 +11,24 @@ func RandBiasedUint64() uint64 {
 
 // Generate a random int64 with an even distribution of the tuple
 // {sign, bits.Len64(math.Abs())}
-func RandBiasedInt64() int64 {
+func RandBiasedInt64() uint64 {
 	shift := rand.Intn(127)
 	// [0,62]: positive
 	// [63,63]: zero
 	// [64,126]: negative
 	if shift < 64 {
-		return int64((rand.Uint64() | 0x8000000000000000) >> (shift + 1))
+		return uint64(int64((rand.Uint64() | 0x8000000000000000) >> (shift + 1)))
 	} else {
-		return int64((rand.Uint64() | 0x8000000000000000) >> (shift - 63)) * -1
+		return uint64(int64((rand.Uint64() | 0x8000000000000000) >> (shift - 63)) * -1)
+	}
+}
+
+// Mixture of RandBiasedUint64() and RandBiasedInt64(), with probability shifted
+// toward more unsigned values.
+func RandBiasedUSint64() uint64 {
+	if rand.Intn(2) == 0 {
+		return RandBiasedUint64()
+	} else {
+		return RandBiasedInt64()
 	}
 }
diff --git a/test/gen_test.go b/test/gen_test.go
new file mode 100644
index 0000000..6a100ff
--- /dev/null
+++ b/test/gen_test.go
@@ -0,0 +1,9 @@
+package test
+
+import "testing"
+
+import "github.com/firestuff/subcoding/gen"
+
+func TestRandProgram(t *testing.T) {
+	gen.RandProgram()
+}
diff --git a/test/rand_test.go b/test/rand_test.go
index 39e6127..d13c54e 100644
--- a/test/rand_test.go
+++ b/test/rand_test.go
@@ -43,7 +43,7 @@ func TestRandBiasedInt64(t *testing.T) {
 	buckets := [127]uint64{}
 
 	for i := 0; i < 1000000; i++ {
-		val := gen.RandBiasedInt64()
+		val := int64(gen.RandBiasedInt64())
 		switch {
 		case val == 0:
 			buckets[63]++