diff --git a/docs/sdk/script/Diagnostics.xml b/docs/sdk/script/Diagnostics.xml
index 246bd90da..290eb1f9a 100644
--- a/docs/sdk/script/Diagnostics.xml
+++ b/docs/sdk/script/Diagnostics.xml
@@ -229,6 +229,24 @@ func g(a, ...) {
           </part>
         </col>
       </row>
+      <row>
+        <col>suspicious_assignment</col>
+        <col>
+          <text>
+            An assignment was found where an expression was expected. While
+            an assignment returns its own value, usually a comparison was
+            intended instead.
+          </text>
+          <part>
+            <code>if (a = b + 1) { /* Do something */}</code>
+          </part>
+          <text>
+            If the assignment is intentional, make this more obvious by
+            extracting it to a separate statement, or explicitly handle the
+            boolean conversion by adding a comparison operator.
+          </text>
+        </col>
+      </row>
     </table>
   </part>
 
diff --git a/src/script/C4AulCompiler.cpp b/src/script/C4AulCompiler.cpp
index 1e2a95725..e76d02187 100644
--- a/src/script/C4AulCompiler.cpp
+++ b/src/script/C4AulCompiler.cpp
@@ -2,7 +2,7 @@
  * OpenClonk, http://www.openclonk.org
  *
  * Copyright (c) 2001-2009, RedWolf Design GmbH, http://www.clonk.de/
- * Copyright (c) 2009-2016, The OpenClonk Team and contributors
+ * Copyright (c) 2009-2018, The OpenClonk Team and contributors
  *
  * Distributed under the terms of the ISC license; see accompanying file
  * "COPYING" for details.
@@ -255,6 +255,14 @@ class C4AulCompiler::CodegenAstVisitor : public ::aul::DefaultRecursiveVisitor
 		}
 	};
 
+	void WarnOnAssignment(const ::aul::ast::ExprPtr &n) const
+	{
+		if (dynamic_cast<const ::aul::ast::AssignmentExpr*>(n.get()) != nullptr)
+		{
+			Warn(target_host, host, n.get(), Fn, C4AulWarningId::suspicious_assignment);
+		}
+	}
+
 public:
 	CodegenAstVisitor(C4ScriptHost *host, C4ScriptHost *source_host) : target_host(host), host(source_host) {}
 	explicit CodegenAstVisitor(C4AulScriptFunc *func) : Fn(func), target_host(func->pOrgScript), host(target_host) {}
@@ -1415,6 +1423,7 @@ void C4AulCompiler::CodegenAstVisitor::visit(const ::aul::ast::Return *n)
 {
 	StackGuard g(this, 0);
 
+	WarnOnAssignment(n->value);
 	SafeVisit(n->value);
 	AddBCC(n->loc, AB_RETURN);
 }
@@ -1442,6 +1451,7 @@ void C4AulCompiler::CodegenAstVisitor::visit(const ::aul::ast::ForLoop *n)
 	PushLoop();
 	if (n->cond)
 	{
+		WarnOnAssignment(n->cond);
 		cond = AddJumpTarget();
 		SafeVisit(n->cond);
 		active_loops.top().breaks.push_back(AddBCC(n->cond->loc, AB_CONDN));
@@ -1560,6 +1570,7 @@ void C4AulCompiler::CodegenAstVisitor::visit(const ::aul::ast::WhileLoop *n)
 {
 	int cond = AddJumpTarget();
 	PushLoop();
+	WarnOnAssignment(n->cond);
 	SafeVisit(n->cond);
 	active_loops.top().breaks.push_back(AddBCC(n->cond->loc, AB_CONDN));
 	if (SafeVisit(n->body))
@@ -1583,6 +1594,7 @@ void C4AulCompiler::CodegenAstVisitor::visit(const ::aul::ast::Continue *n)
 
 void C4AulCompiler::CodegenAstVisitor::visit(const ::aul::ast::If *n)
 {
+	WarnOnAssignment(n->cond);
 	SafeVisit(n->cond);
 	int jump = AddBCC(n->loc, AB_CONDN);
 	// Warn if we're controlling a no-op ("if (...);")
diff --git a/src/script/C4AulWarnings.h b/src/script/C4AulWarnings.h
index bea1236e2..02bd78ede 100644
--- a/src/script/C4AulWarnings.h
+++ b/src/script/C4AulWarnings.h
@@ -1,7 +1,7 @@
 /*
 * OpenClonk, http://www.openclonk.org
 *
-* Copyright (c) 2017, The OpenClonk Team and contributors
+* Copyright (c) 2017-2018, The OpenClonk Team and contributors
 *
 * Distributed under the terms of the ISC license; see accompanying file
 * "COPYING" for details.
@@ -38,5 +38,6 @@ DIAG(undeclared_varargs, "use of '%s' in a function forces it to take variable a
 DIAG(arg_count_mismatch, "call to '%s' passes %u arguments, of which only %u are used", true)
 DIAG(arg_type_mismatch, "parameter %u of call to '%s' passes %s (%s expected)", true)
 DIAG(empty_if, "empty controlled statement (use '{}' if this is intentional)", true)
+DIAG(suspicious_assignment, "suspicious assignment (was a comparison intended here?)", true)
 
 #pragma pop_macro("DIAG")
diff --git a/tests/aul/AulDiagnosticsTest.cpp b/tests/aul/AulDiagnosticsTest.cpp
index d27801670..751d5b165 100644
--- a/tests/aul/AulDiagnosticsTest.cpp
+++ b/tests/aul/AulDiagnosticsTest.cpp
@@ -1,7 +1,7 @@
 /*
  * OpenClonk, http://www.openclonk.org
  *
- * Copyright (c) 2015-2017, The OpenClonk Team and contributors
+ * Copyright (c) 2015-2018, The OpenClonk Team and contributors
  *
  * Distributed under the terms of the ISC license; see accompanying file
  * "COPYING" for details.
@@ -85,6 +85,50 @@ TEST_F(AulDiagnosticsTest, empty_if)
 	}
 }
 
+TEST_F(AulDiagnosticsTest, suspicious_assignment)
+{
+	{
+		EXPECT_WARNING(suspicious_assignment);
+		RunCode("var a = 0; if (a = 0) {}");
+	}
+	{
+		EXPECT_WARNING(suspicious_assignment).Times(0);
+		RunCode("var a = 0; if (a == 1) {}");
+		RunCode("var a = 0; if (a += 1) {}");
+	}
+	{
+		EXPECT_WARNING(suspicious_assignment);
+		RunCode("for (var a = 0; a = 0;) {}");
+	}
+	{
+		EXPECT_WARNING(suspicious_assignment).Times(0);
+		RunCode("for (var a = 0; a == 1;) {}");
+		RunCode("for (var a = 0; a != 0;) {}");
+	}
+	{
+		EXPECT_WARNING(suspicious_assignment);
+		RunCode("var a = 0; while (a = 0) {}");
+	}
+	{
+		EXPECT_WARNING(suspicious_assignment).Times(0);
+		RunCode("var a = 0; while (a == 1) {}");
+		RunCode("var a = 0; while (a *= 1) {}");
+	}
+	{
+		EXPECT_WARNING(suspicious_assignment);
+		RunCode("var a = 0; return a = 0;");
+	}
+	{
+		EXPECT_WARNING(suspicious_assignment);
+		RunCode("var a = 0; return (a = 0);");
+	}
+	{
+		EXPECT_WARNING(suspicious_assignment).Times(0);
+		RunCode("var a = 0; return a == 0;");
+		RunCode("var a = 0; return (a = 0) == 0;");
+	}
+}
+
 TEST_F(AulDiagnosticsTest, arg_count_mismatch)
 {
 	{