diff --git a/nested_blocks_test.go b/nested_blocks_test.go
new file mode 100644
index 0000000..74e8c91
--- /dev/null
+++ b/nested_blocks_test.go
@@ -0,0 +1,204 @@
+package twig
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestBlocksInConditionals(t *testing.T) {
+	tests := []struct {
+		name      string
+		base      string
+		extend    string
+		expected  string
+		shouldErr bool
+	}{
+		{
+			name: "block inside if condition",
+			base: `{% if true %}
+		{% block my_block %}foo{% endblock %}
+	{% endif %}`,
+			extend: `{% extends "base" %}
+
+	{% block my_block %}
+		<p>{{ parent() }}</p>
+	{% endblock %}`,
+			expected: `<p>foo</p>`,
+		},
+		{
+			name: "block inside else branch",
+			base: `{% if false %}
+		nothing
+	{% else %}
+		{% block my_block %}bar{% endblock %}
+	{% endif %}`,
+			extend: `{% extends "base" %}
+
+	{% block my_block %}
+		<div>{{ parent() }}</div>
+	{% endblock %}`,
+			expected: `<div>bar</div>`,
+		},
+		{
+			name: "block inside nested if",
+			base: `{% if true %}
+		{% if true %}
+			{% block my_block %}nested{% endblock %}
+		{% endif %}
+	{% endif %}`,
+			extend: `{% extends "base" %}
+
+	{% block my_block %}
+		{{ parent() }}-extended
+	{% endblock %}`,
+			expected: `nested-extended`,
+		},
+		{
+			name: "block inside for loop",
+			base: `{% for i in [1] %}
+		{% block my_block %}loop{{ i }}{% endblock %}
+	{% endfor %}`,
+			extend: `{% extends "base" %}
+
+	{% block my_block %}
+		prefix-{{ parent() }}
+	{% endblock %}`,
+			expected: `prefix-loop1`,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			engine := New()
+			loader := NewArrayLoader(map[string]string{
+				"base":   tt.base,
+				"extend": tt.extend,
+			})
+			engine.RegisterLoader(loader)
+
+			result, err := engine.Render("extend", nil)
+			if err != nil {
+				if !tt.shouldErr {
+					t.Fatalf("unexpected error: %v", err)
+				}
+				return
+			}
+
+			if tt.shouldErr {
+				t.Fatal("expected error but got none")
+			}
+
+			// Normalize whitespace for comparison
+			result = strings.TrimSpace(result)
+			expected := strings.TrimSpace(tt.expected)
+
+			// Remove extra whitespace
+			result = strings.Join(strings.Fields(result), " ")
+			expected = strings.Join(strings.Fields(expected), " ")
+
+			if result != expected {
+				t.Errorf("expected %q, got %q", expected, result)
+			}
+		})
+	}
+}
+
+func TestBlocksInApplyFilter(t *testing.T) {
+	tests := []struct {
+		name      string
+		base      string
+		extend    string
+		expected  string
+		shouldErr bool
+	}{
+		{
+			name: "block inside apply spaceless",
+			base: `{% apply spaceless %}
+		{% block my_block %}foo{% endblock %}
+	{% endapply %}`,
+			extend: `{% extends "base" %}
+
+	{% block my_block %}
+		<p>{{ parent() }}</p>
+	{% endblock %}`,
+			expected: `<p>foo</p>`,
+		},
+		{
+			name: "block inside apply upper",
+			base: `{% apply upper %}
+		{% block my_block %}hello{% endblock %}
+	{% endapply %}`,
+			extend: `{% extends "base" %}
+
+	{% block my_block %}
+		{{ parent() }} world
+	{% endblock %}`,
+			expected: `HELLO WORLD`,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			engine := New()
+			loader := NewArrayLoader(map[string]string{
+				"base":   tt.base,
+				"extend": tt.extend,
+			})
+			engine.RegisterLoader(loader)
+
+			result, err := engine.Render("extend", nil)
+			if err != nil {
+				if !tt.shouldErr {
+					t.Fatalf("unexpected error: %v", err)
+				}
+				return
+			}
+
+			if tt.shouldErr {
+				t.Fatal("expected error but got none")
+			}
+
+			// Normalize whitespace for comparison
+			result = strings.TrimSpace(result)
+			expected := strings.TrimSpace(tt.expected)
+
+			if result != expected {
+				t.Errorf("expected %q, got %q", expected, result)
+			}
+		})
+	}
+}
+
+func TestComplexNestedBlocks(t *testing.T) {
+	// Test the exact example from the issue
+	engine := New()
+	loader := NewArrayLoader(map[string]string{
+		"base": `
+		{% apply spaceless %}
+			{% block my_block %}foo{% endblock %}
+		{% endapply %}
+`,
+		"extend": `
+		{% extends "base" %}
+
+		{% block my_block %}
+			<p>{{ parent() }}</p>
+		{% endblock %}
+`,
+	})
+
+	engine.RegisterLoader(loader)
+	result, err := engine.Render("extend", nil)
+
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// The expected result with spaceless applied
+	expected := "<p>foo</p>"
+	result = strings.TrimSpace(result)
+
+	if result != expected {
+		t.Errorf("expected %q, got %q", expected, result)
+	}
+}