diff --git a/src/main/scala/millfork/compiler/AbstractStatementPreprocessor.scala b/src/main/scala/millfork/compiler/AbstractStatementPreprocessor.scala
index dd29703e..1224e7ff 100644
--- a/src/main/scala/millfork/compiler/AbstractStatementPreprocessor.scala
+++ b/src/main/scala/millfork/compiler/AbstractStatementPreprocessor.scala
@@ -2,7 +2,6 @@ package millfork.compiler
 
 import millfork.CompilationFlag
 import millfork.env._
-import millfork.error.ConsoleLogger
 import millfork.node._
 import AbstractExpressionCompiler.getExpressionType
 import millfork.compiler.AbstractStatementPreprocessor.hiddenEffectFreeFunctions
@@ -60,6 +59,20 @@ abstract class AbstractStatementPreprocessor(ctx: CompilationContext, statements
   def optimizeStmt(stmt: ExecutableStatement, currentVarValues: VV): (ExecutableStatement, VV) = {
     var cv = currentVarValues
     val pos = stmt.position
+    // generic warnings:
+    stmt match {
+      case ExpressionStatement(expr@FunctionCallExpression("strzlen" | "putstrz", List(TextLiteralExpression(ch)))) =>
+        ch.last match {
+          case LiteralExpression(0, _) => //ok
+          case _ => ctx.log.warn("Passing a non-null-terminated string to a function that expects a null-terminated string.", stmt.position)
+        }
+      case ExpressionStatement(VariableExpression(v)) =>
+        val volatile = ctx.env.maybeGet[ThingInMemory](v).fold(false)(_.isVolatile)
+        if (!volatile) ctx.log.warn("Pointless expression.", stmt.position)
+      case ExpressionStatement(LiteralExpression(_, _)) =>
+        ctx.log.warn("Pointless expression.", stmt.position)
+      case _ =>
+    }
     stmt match {
       case Assignment(ve@VariableExpression(v), arg) if trackableVars(v) =>
         cv = search(arg, cv)
@@ -164,6 +177,17 @@ abstract class AbstractStatementPreprocessor(ctx: CompilationContext, statements
 
   def optimizeExpr(expr: Expression, currentVarValues: VV): Expression = {
     val pos = expr.position
+    // generic warnings:
+    expr match {
+      case FunctionCallExpression("*" | "*=", params) =>
+        if (params.exists {
+          case LiteralExpression(0, _) => true
+          case _ => false
+        }) ctx.log.warn("Multiplication by zero.", params.head.position)
+      case FunctionCallExpression("<<" | ">>" | "<<'" | "<<=" | ">>=" | "<<'=" | ">>>>", List(lhs@_, LiteralExpression(0, _))) =>
+        ctx.log.warn("Shift by zero.", lhs.position)
+      case _ =>
+    }
     expr match {
       case FunctionCallExpression("->", List(handle, VariableExpression(field))) =>
         expr
diff --git a/src/main/scala/millfork/env/Environment.scala b/src/main/scala/millfork/env/Environment.scala
index 550874a5..28f22320 100644
--- a/src/main/scala/millfork/env/Environment.scala
+++ b/src/main/scala/millfork/env/Environment.scala
@@ -712,6 +712,14 @@ class Environment(val parent: Option[Environment], val prefix: String, val cpuFa
     val w = get[Type]("word")
     val name = stmt.name
     val resultType = get[Type](stmt.resultType)
+    if (stmt.name == "main") {
+      if (stmt.resultType != "void") {
+        log.warn("`main` should return `void`.", stmt.position)
+      }
+      if (stmt.params.nonEmpty) {
+        log.warn("`main` shouldn't have parameters.", stmt.position)
+      }
+    }
 
     if (stmt.reentrant && stmt.interrupt) log.error(s"Reentrant function `$name` cannot be an interrupt handler", stmt.position)
     if (stmt.reentrant && stmt.params.nonEmpty) log.error(s"Reentrant function `$name` cannot have parameters", stmt.position)
@@ -812,7 +820,7 @@ class Environment(val parent: Option[Environment], val prefix: String, val cpuFa
             env,
             stackVariablesSize,
             stmt.address.map(a => this.eval(a).getOrElse(errorConstant(s"Address of `${stmt.name}` is not a constant"))),
-            executableStatements ++ (if (needsExtraRTS) List(ReturnStatement(None)) else Nil),
+            executableStatements ++ (if (needsExtraRTS) List(ReturnStatement(None).pos(executableStatements.lastOption.fold(stmt.position)(_.position))) else Nil),
             interrupt = stmt.interrupt,
             kernalInterrupt = stmt.kernalInterrupt,
             reentrant = stmt.reentrant,
diff --git a/src/test/scala/millfork/test/WarningSuite.scala b/src/test/scala/millfork/test/WarningSuite.scala
new file mode 100644
index 00000000..b349eeaa
--- /dev/null
+++ b/src/test/scala/millfork/test/WarningSuite.scala
@@ -0,0 +1,30 @@
+package millfork.test
+
+import millfork.Cpu
+import millfork.test.emu.EmuUnoptimizedCrossPlatformRun
+import org.scalatest.{FunSuite, Matchers}
+
+/**
+  * @author Karol Stasiak
+  */
+class WarningSuite extends FunSuite with Matchers {
+
+  test("Various warnings") {
+    EmuUnoptimizedCrossPlatformRun(Cpu.Mos, Cpu.Z80)(
+      """
+        | void putstrz(pointer p) {}
+        | byte output@0xc000
+        | byte main (byte x) {
+        |  putstrz("a")
+        |  byte a
+        |  a
+        |  5
+        |  a *= 0
+        |  a <<= 0
+        |  output = 4
+        | }
+      """.stripMargin) { m =>
+      m.readByte(0xc000) should equal(4)
+    }
+  }
+}