diff --git a/pkg/compiler/analysis.go b/pkg/compiler/analysis.go
index 730a9bd89..cd9e9148d 100644
--- a/pkg/compiler/analysis.go
+++ b/pkg/compiler/analysis.go
@@ -14,7 +14,7 @@ import (
 
 var (
 	// Go language builtin functions.
-	goBuiltins = []string{"len", "append", "panic", "make", "copy", "recover"}
+	goBuiltins = []string{"len", "append", "panic", "make", "copy", "recover", "delete"}
 	// Custom builtin utility functions.
 	customBuiltins = []string{
 		"FromAddress", "Equals",
@@ -109,8 +109,17 @@ func countGlobals(f ast.Node) (i int) {
 			return false
 		// After skipping all funcDecls we are sure that each value spec
 		// is a global declared variable or constant.
-		case *ast.ValueSpec:
-			i += len(n.Names)
+		case *ast.GenDecl:
+			if n.Tok == token.VAR {
+				for _, s := range n.Specs {
+					for _, id := range s.(*ast.ValueSpec).Names {
+						if id.Name != "_" {
+							i++
+						}
+					}
+				}
+			}
+			return false
 		}
 		return true
 	})
diff --git a/pkg/compiler/codegen.go b/pkg/compiler/codegen.go
index 710d58de6..be9e8ec2c 100644
--- a/pkg/compiler/codegen.go
+++ b/pkg/compiler/codegen.go
@@ -434,13 +434,15 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 			switch t := spec.(type) {
 			case *ast.ValueSpec:
 				for _, id := range t.Names {
-					if c.scope == nil {
-						// it is a global declaration
-						c.newGlobal("", id.Name)
-					} else {
-						c.scope.newLocal(id.Name)
+					if id.Name != "_" {
+						if c.scope == nil {
+							// it is a global declaration
+							c.newGlobal("", id.Name)
+						} else {
+							c.scope.newLocal(id.Name)
+						}
+						c.registerDebugVariable(id.Name, t.Type)
 					}
-					c.registerDebugVariable(id.Name, t.Type)
 				}
 				for i := range t.Names {
 					if len(t.Values) != 0 {
@@ -1525,6 +1527,8 @@ func (c *codegen) convertBuiltin(expr *ast.CallExpr) {
 		}
 		emit.Opcode(c.prog.BinWriter, opcode.PUSHNULL)
 		c.emitStoreByIndex(varGlobal, c.exceptionIndex)
+	case "delete":
+		emit.Opcode(c.prog.BinWriter, opcode.REMOVE)
 	case "ToInteger", "ToByteArray", "ToBool":
 		typ := stackitem.IntegerT
 		switch name {
diff --git a/pkg/compiler/global_test.go b/pkg/compiler/global_test.go
index e4f29f89b..434c22290 100644
--- a/pkg/compiler/global_test.go
+++ b/pkg/compiler/global_test.go
@@ -1,6 +1,7 @@
 package compiler_test
 
 import (
+	"bytes"
 	"fmt"
 	"math/big"
 	"strings"
@@ -238,3 +239,35 @@ func TestMultipleFuncSameName(t *testing.T) {
 		eval(t, src, big.NewInt(42))
 	})
 }
+
+func TestConstDontUseSlots(t *testing.T) {
+	const count = 256
+	buf := bytes.NewBufferString("package foo\n")
+	for i := 0; i < count; i++ {
+		buf.WriteString(fmt.Sprintf("const n%d = 1\n", i))
+	}
+	buf.WriteString("func Main() int { sum := 0\n")
+	for i := 0; i < count; i++ {
+		buf.WriteString(fmt.Sprintf("sum += n%d\n", i))
+	}
+	buf.WriteString("return sum }")
+
+	src := buf.String()
+	eval(t, src, big.NewInt(count))
+}
+
+func TestUnderscoreVarsDontUseSlots(t *testing.T) {
+	const count = 128
+	buf := bytes.NewBufferString("package foo\n")
+	for i := 0; i < count; i++ {
+		buf.WriteString(fmt.Sprintf("var _, n%d = 1, 1\n", i))
+	}
+	buf.WriteString("func Main() int { sum := 0\n")
+	for i := 0; i < count; i++ {
+		buf.WriteString(fmt.Sprintf("sum += n%d\n", i))
+	}
+	buf.WriteString("return sum }")
+
+	src := buf.String()
+	eval(t, src, big.NewInt(count))
+}
diff --git a/pkg/compiler/map_test.go b/pkg/compiler/map_test.go
index be7453507..30fcf85a2 100644
--- a/pkg/compiler/map_test.go
+++ b/pkg/compiler/map_test.go
@@ -55,6 +55,26 @@ var mapTestCases = []testCase{
 		`,
 		[]byte("Valera"),
 	},
+	{
+		"delete key",
+		`package foo
+		func Main() int {
+			m := map[int]int{1: 2, 3: 4}
+			delete(m, 1)
+			return len(m)
+		}`,
+		big.NewInt(1),
+	},
+	{
+		"delete missing key",
+		`package foo
+		func Main() int {
+			m := map[int]int{3: 4}
+			delete(m, 1)
+			return len(m)
+		}`,
+		big.NewInt(1),
+	},
 }
 
 func TestMaps(t *testing.T) {