diff --git a/cli/command/image/build/internal/urlutil/urlutil.go b/cli/command/image/build/internal/urlutil/urlutil.go
index b1cf47ce316b..11f02f2a0f91 100644
--- a/cli/command/image/build/internal/urlutil/urlutil.go
+++ b/cli/command/image/build/internal/urlutil/urlutil.go
@@ -19,6 +19,7 @@ var urlPathWithFragmentSuffix = lazyregexp.New(`\.git(?:#.+)?$`)
 // has a http:// or https:// scheme. No validation is performed to verify if the
 // URL is well-formed.
 func IsURL(str string) bool {
+	str = strings.ToLower(str)
 	return strings.HasPrefix(str, "https://") || strings.HasPrefix(str, "http://")
 }
 
diff --git a/cli/command/image/build/internal/urlutil/urlutil_test.go b/cli/command/image/build/internal/urlutil/urlutil_test.go
index f6d0a35de3ec..7ad0f5a41b0f 100644
--- a/cli/command/image/build/internal/urlutil/urlutil_test.go
+++ b/cli/command/image/build/internal/urlutil/urlutil_test.go
@@ -40,3 +40,22 @@ func TestIsGIT(t *testing.T) {
 		}
 	}
 }
+
+func TestIsURL(t *testing.T) {
+	tests := []struct {
+		url  string
+		want bool
+	}{
+		{"https://example.com/context.tar", true},
+		{"http://example.com/context.tar", true},
+		{"HTTPS://example.com/context.tar", true},
+		{"HTTP://example.com/context.tar", true},
+		{"/tmp/context.tar", false},
+	}
+
+	for _, tt := range tests {
+		if got := IsURL(tt.url); got != tt.want {
+			t.Errorf("IsURL(%q) = %t, want %t", tt.url, got, tt.want)
+		}
+	}
+}