diff --git a/absl/time/duration.cc b/absl/time/duration.cc
index 31b7bf2a1f7..19407080a7f 100644
--- a/absl/time/duration.cc
+++ b/absl/time/duration.cc
@@ -549,50 +549,6 @@ Duration DurationFromTimeval(timeval tv) {
 //
 // Conversion to other duration types.
 //
-
-int64_t ToInt64Nanoseconds(Duration d) {
-  if (time_internal::GetRepHi(d) >= 0 &&
-      time_internal::GetRepHi(d) >> 33 == 0) {
-    return (time_internal::GetRepHi(d) * 1000 * 1000 * 1000) +
-           (time_internal::GetRepLo(d) / kTicksPerNanosecond);
-  }
-  return d / Nanoseconds(1);
-}
-int64_t ToInt64Microseconds(Duration d) {
-  if (time_internal::GetRepHi(d) >= 0 &&
-      time_internal::GetRepHi(d) >> 43 == 0) {
-    return (time_internal::GetRepHi(d) * 1000 * 1000) +
-           (time_internal::GetRepLo(d) / (kTicksPerNanosecond * 1000));
-  }
-  return d / Microseconds(1);
-}
-int64_t ToInt64Milliseconds(Duration d) {
-  if (time_internal::GetRepHi(d) >= 0 &&
-      time_internal::GetRepHi(d) >> 53 == 0) {
-    return (time_internal::GetRepHi(d) * 1000) +
-           (time_internal::GetRepLo(d) / (kTicksPerNanosecond * 1000 * 1000));
-  }
-  return d / Milliseconds(1);
-}
-int64_t ToInt64Seconds(Duration d) {
-  int64_t hi = time_internal::GetRepHi(d);
-  if (time_internal::IsInfiniteDuration(d)) return hi;
-  if (hi < 0 && time_internal::GetRepLo(d) != 0) ++hi;
-  return hi;
-}
-int64_t ToInt64Minutes(Duration d) {
-  int64_t hi = time_internal::GetRepHi(d);
-  if (time_internal::IsInfiniteDuration(d)) return hi;
-  if (hi < 0 && time_internal::GetRepLo(d) != 0) ++hi;
-  return hi / 60;
-}
-int64_t ToInt64Hours(Duration d) {
-  int64_t hi = time_internal::GetRepHi(d);
-  if (time_internal::IsInfiniteDuration(d)) return hi;
-  if (hi < 0 && time_internal::GetRepLo(d) != 0) ++hi;
-  return hi / (60 * 60);
-}
-
 double ToDoubleNanoseconds(Duration d) {
   return FDivDuration(d, Nanoseconds(1));
 }
diff --git a/absl/time/time.h b/absl/time/time.h
index 4f88c304d77..d73a204c12c 100644
--- a/absl/time/time.h
+++ b/absl/time/time.h
@@ -620,12 +620,12 @@ ABSL_ATTRIBUTE_CONST_FUNCTION Duration Hours(T n) {
 //
 //   absl::Duration d = absl::Milliseconds(1500);
 //   int64_t isec = absl::ToInt64Seconds(d);  // isec == 1
-ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Nanoseconds(Duration d);
-ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Microseconds(Duration d);
-ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Milliseconds(Duration d);
-ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Seconds(Duration d);
-ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Minutes(Duration d);
-ABSL_ATTRIBUTE_CONST_FUNCTION int64_t ToInt64Hours(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Nanoseconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Microseconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Milliseconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Seconds(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Minutes(Duration d);
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Hours(Duration d);
 
 // ToDoubleNanoseconds()
 // ToDoubleMicroseconds()
@@ -1864,6 +1864,56 @@ ABSL_ATTRIBUTE_CONST_FUNCTION constexpr Time FromTimeT(time_t t) {
   return time_internal::FromUnixDuration(Seconds(t));
 }
 
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Nanoseconds(Duration d) {
+  if (time_internal::GetRepHi(d) >= 0 &&
+      time_internal::GetRepHi(d) >> 33 == 0) {
+    return (time_internal::GetRepHi(d) * 1000 * 1000 * 1000) +
+           (time_internal::GetRepLo(d) / time_internal::kTicksPerNanosecond);
+  }
+  return d / Nanoseconds(1);
+}
+
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Microseconds(Duration d) {
+  if (time_internal::GetRepHi(d) >= 0 &&
+      time_internal::GetRepHi(d) >> 43 == 0) {
+    return (time_internal::GetRepHi(d) * 1000 * 1000) +
+           (time_internal::GetRepLo(d) /
+            (time_internal::kTicksPerNanosecond * 1000));
+  }
+  return d / Microseconds(1);
+}
+
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Milliseconds(Duration d) {
+  if (time_internal::GetRepHi(d) >= 0 &&
+      time_internal::GetRepHi(d) >> 53 == 0) {
+    return (time_internal::GetRepHi(d) * 1000) +
+           (time_internal::GetRepLo(d) /
+            (time_internal::kTicksPerNanosecond * 1000 * 1000));
+  }
+  return d / Milliseconds(1);
+}
+
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Seconds(Duration d) {
+  int64_t hi = time_internal::GetRepHi(d);
+  if (time_internal::IsInfiniteDuration(d)) return hi;
+  if (hi < 0 && time_internal::GetRepLo(d) != 0) ++hi;
+  return hi;
+}
+
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Minutes(Duration d) {
+  int64_t hi = time_internal::GetRepHi(d);
+  if (time_internal::IsInfiniteDuration(d)) return hi;
+  if (hi < 0 && time_internal::GetRepLo(d) != 0) ++hi;
+  return hi / 60;
+}
+
+ABSL_ATTRIBUTE_CONST_FUNCTION inline int64_t ToInt64Hours(Duration d) {
+  int64_t hi = time_internal::GetRepHi(d);
+  if (time_internal::IsInfiniteDuration(d)) return hi;
+  if (hi < 0 && time_internal::GetRepLo(d) != 0) ++hi;
+  return hi / (60 * 60);
+}
+
 ABSL_NAMESPACE_END
 }  // namespace absl