diff --git a/compiler/src/dotty/tools/dotc/typer/Checking.scala b/compiler/src/dotty/tools/dotc/typer/Checking.scala
index c402f4aafccf..7cb144adb025 100644
--- a/compiler/src/dotty/tools/dotc/typer/Checking.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Checking.scala
@@ -315,7 +315,10 @@ object Checking {
         fail(AbstractMemberMayNotHaveModifier(sym, flag))
     def checkNoConflict(flag1: FlagSet, flag2: FlagSet) =
       if (sym.is(allOf(flag1, flag2)))
-        fail(i"illegal combination of modifiers: $flag1 and $flag2 for: $sym")
+        fail(i"illegal combination of modifiers: `$flag1` and `$flag2` for: $sym")
+    def checkApplicable(flag: FlagSet, ok: Boolean) =
+      if (!ok && !sym.is(Synthetic))
+        fail(i"modifier `$flag` is not allowed for this definition")
 
     if (sym.is(ImplicitCommon)) {
       if (sym.owner.is(Package))
@@ -345,6 +348,9 @@ object Checking {
     checkNoConflict(Final, Sealed)
     checkNoConflict(Private, Protected)
     checkNoConflict(Abstract, Override)
+    checkNoConflict(Lazy, Inline)
+    if (sym.is(Inline)) checkApplicable(Inline, sym.isTerm && !sym.is(Mutable | Module))
+    if (sym.is(Lazy)) checkApplicable(Lazy, !sym.is(Method | Mutable))
     if (sym.isType && !sym.is(Deferred))
       for (cls <- sym.allOverriddenSymbols.filter(_.isClass)) {
         fail(CannotHaveSameNameAs(sym, cls, CannotHaveSameNameAs.CannotBeOverridden))
diff --git a/compiler/src/dotty/tools/dotc/typer/Namer.scala b/compiler/src/dotty/tools/dotc/typer/Namer.scala
index 74cfffbcd6a1..5038007b4ec0 100644
--- a/compiler/src/dotty/tools/dotc/typer/Namer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Namer.scala
@@ -243,6 +243,10 @@ class Namer { typer: Typer =>
     def privateWithinClass(mods: Modifiers) =
       enclosingClassNamed(mods.privateWithin, mods.pos)
 
+    /** Check that flags are OK for symbol. This is done early to avoid
+     *  catastrophic failure when we create a TermSymbol with TypeFlags, or vice versa.
+     *  A more complete check is done in checkWellformed.
+     */
     def checkFlags(flags: FlagSet) =
       if (flags.isEmpty) flags
       else {
diff --git a/tests/neg/i2421.scala b/tests/neg/i2421.scala
new file mode 100644
index 000000000000..c09da6a8a3f2
--- /dev/null
+++ b/tests/neg/i2421.scala
@@ -0,0 +1,10 @@
+inline object Foo // error: modifier(s) `inline' incompatible with type definition
+inline class Bar // error: modifier(s) `inline' incompatible with type definition
+inline abstract class Baz // error: modifier(s) `inline' incompatible with type definition
+inline trait Qux // error: modifier(s) `inline' incompatible with type definition
+
+object Quux {
+  inline type T // error: modifier(s) `inline' incompatible with type definition
+  inline var x: Int = 42 // error: modifier(s) `inline' incompatible with var definition
+  inline lazy val y: Int = 43 // error: modifier(s) `inline' incompatible with lazy val definition
+}
diff --git a/tests/neg/i2712.scala b/tests/neg/i2712.scala
new file mode 100644
index 000000000000..59fb0a1ebf14
--- /dev/null
+++ b/tests/neg/i2712.scala
@@ -0,0 +1,12 @@
+object Foo {
+  lazy var x: Int = 42 // error: modifier(s) `lazy' incompatible with var definition
+  lazy def y: Int = 42 // error: modifier(s) `lazy' incompatible with def definition
+}
+
+lazy class Bar // error: modifier(s) `lazy' incompatible with type definition
+lazy abstract class Baz // error: modifier(s) `lazy abstract' incompatible with type definition
+lazy trait Qux // error: modifier(s) `lazy' not allowed for trait
+
+object Quux {
+  lazy type T // error: modifier(s) `lazy' incompatible with type definition
+}