diff --git a/openrtb2/banner.go b/openrtb2/banner.go
index d3a5254..ea15c8a 100644
--- a/openrtb2/banner.go
+++ b/openrtb2/banner.go
@@ -123,8 +123,8 @@ type Banner struct {
 	//   integer
 	// Description:
 	//   Indicates if the banner is in the top frame as opposed to an
-	//   iframe, where 0 = no, 1 = yes.
-	TopFrame int8 `json:"topframe,omitempty"`
+	//   iframe, where 0 = no, 1 = yes, omission indicates Unknown.
+	TopFrame *int8 `json:"topframe,omitempty"`
 
 	// Attribute:
 	//   expdir
diff --git a/openrtb2/regs.go b/openrtb2/regs.go
index a19c6d7..5ba4052 100644
--- a/openrtb2/regs.go
+++ b/openrtb2/regs.go
@@ -14,9 +14,10 @@ type Regs struct {
 	//   integer
 	// Description:
 	//   Flag indicating if this request is subject to the COPPA
-	//   regulations established by the USA FTC, where 0 = no, 1 = yes.
-	//   Refer to Section 7.5 for more information.
-	COPPA int8 `json:"coppa,omitempty"`
+	//   regulations established by the USA FTC, where 0 = no, 1 = yes,
+	//   omission indicates Unknown. Refer to Section 7.5 for more
+	//   information.
+	COPPA *int8 `json:"coppa,omitempty"`
 
 	// Attribute:
 	//   gdpr
diff --git a/openrtb2/video.go b/openrtb2/video.go
index 79be589..bd677b2 100644
--- a/openrtb2/video.go
+++ b/openrtb2/video.go
@@ -276,8 +276,9 @@ type Video struct {
 	// Type:
 	//   integer
 	// Description:
-	//   Minimum bit rate in Kbps (kilobits per second).
-	MinBitRate int64 `json:"minbitrate,omitempty"`
+	//   Minimum bit rate in Kbps (kilobits per second). A value of 0 is
+	//   a meaningful floor, distinct from omitting the attribute.
+	MinBitRate *int64 `json:"minbitrate,omitempty"`
 
 	// Attribute:
 	//   maxbitrate
diff --git a/openrtb2/zero_value_fields_test.go b/openrtb2/zero_value_fields_test.go
new file mode 100644
index 0000000..917feb4
--- /dev/null
+++ b/openrtb2/zero_value_fields_test.go
@@ -0,0 +1,46 @@
+package openrtb2_test
+
+import (
+	"encoding/json"
+
+	. "github.com/prebid/openrtb/v20/openrtb2"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+// These fields (Regs.COPPA, Banner.TopFrame, Video.MinBitRate) were previously typed as
+// plain int8/int64 with `omitempty`. Because encoding/json's omitempty treats a value type's
+// zero value as empty, explicitly setting one of these fields to a meaningful 0 (COPPA: not
+// subject to COPPA, TopFrame: not in the top frame, MinBitRate: a real 0 Kbps floor) was
+// indistinguishable, once marshaled, from never having set the field at all - the sender's
+// explicit signal was silently dropped. See https://github.com/prebid/openrtb/issues/13.
+//
+// Changing them to pointer types (matching the existing pattern used by Regs.GDPR,
+// Banner.Vcm, and Device.DNT for the same "0/1, omission means Unknown" semantics) lets a
+// caller distinguish "not set" (nil) from "explicitly set to 0" (Int8Ptr(0)/Int64Ptr(0)).
+var _ = Describe("Zero-valued optional fields survive marshaling", func() {
+	It("keeps Regs.COPPA when explicitly set to 0", func() {
+		b, err := json.Marshal(Regs{COPPA: Int8Ptr(0)})
+		Expect(err).NotTo(HaveOccurred())
+		Expect(b).To(MatchJSON(`{"coppa":0}`))
+	})
+
+	It("omits Regs.COPPA when left unset", func() {
+		b, err := json.Marshal(Regs{})
+		Expect(err).NotTo(HaveOccurred())
+		Expect(b).To(MatchJSON(`{}`))
+	})
+
+	It("keeps Banner.TopFrame when explicitly set to 0", func() {
+		b, err := json.Marshal(Banner{TopFrame: Int8Ptr(0)})
+		Expect(err).NotTo(HaveOccurred())
+		Expect(b).To(MatchJSON(`{"topframe":0}`))
+	})
+
+	It("keeps Video.MinBitRate when explicitly set to 0", func() {
+		b, err := json.Marshal(Video{MinBitRate: Int64Ptr(0)})
+		Expect(err).NotTo(HaveOccurred())
+		Expect(b).To(MatchJSON(`{"mimes":null,"minbitrate":0}`))
+	})
+})