diff --git a/icu4c/source/common/unicode/locid.h b/icu4c/source/common/unicode/locid.h
index 8d37af680eb8..1ef15ca75120 100644
--- a/icu4c/source/common/unicode/locid.h
+++ b/icu4c/source/common/unicode/locid.h
@@ -1058,12 +1058,12 @@ class U_COMMON_API Locale : public UObject {
 
     /**
      * A friend to allow the default locale to be set by either the C or C++ API.
-     * @internal
+     * @internal (private)
      */
     friend Locale *locale_set_default_internal(const char *, UErrorCode& status);
 
     /**
-     * @internal
+     * @internal (private)
      */
     friend void U_CALLCONV locale_available_init();
 };
diff --git a/icu4c/source/common/unicode/rbbi.h b/icu4c/source/common/unicode/rbbi.h
index e9b82cd52073..47abd554eaf0 100644
--- a/icu4c/source/common/unicode/rbbi.h
+++ b/icu4c/source/common/unicode/rbbi.h
@@ -99,7 +99,7 @@ class U_COMMON_API RuleBasedBreakIterator /*U_FINAL*/ : public BreakIterator {
      * If present, UStack of LanguageBreakEngine objects that might handle
      * dictionary characters. Searched from top to bottom to find an object to
      * handle a given character.
-     * @internal
+     * @internal (private)
      */
     UStack              *fLanguageBreakEngines;
 
@@ -108,14 +108,14 @@ class U_COMMON_API RuleBasedBreakIterator /*U_FINAL*/ : public BreakIterator {
      * If present, the special LanguageBreakEngine used for handling
      * characters that are in the dictionary set, but not handled by any
      * LangugageBreakEngine.
-     * @internal
+     * @internal (private)
      */
     UnhandledEngine     *fUnhandledBreakEngine;
 
     /**
      * Counter for the number of characters encountered with the "dictionary"
      *   flag set.
-     * @internal
+     * @internal (private)
      */
     uint32_t            fDictionaryCharCount;
 
@@ -150,7 +150,7 @@ class U_COMMON_API RuleBasedBreakIterator /*U_FINAL*/ : public BreakIterator {
      *
      *             The break iterator adopts the memory, and will
      *             free it when done.
-     * @internal
+     * @internal (private)
      */
     RuleBasedBreakIterator(RBBIDataHeader* data, UErrorCode &status);
 
diff --git a/icu4c/source/common/unicode/ucptrie.h b/icu4c/source/common/unicode/ucptrie.h
index 461c47a4f2ea..2718c984e431 100644
--- a/icu4c/source/common/unicode/ucptrie.h
+++ b/icu4c/source/common/unicode/ucptrie.h
@@ -598,6 +598,7 @@ enum {
 };
 
 /* Internal functions and macros -------------------------------------------- */
+// Do not conditionalize with #ifndef U_HIDE_INTERNAL_API, needed for public API
 
 /** @internal */
 U_INTERNAL int32_t U_EXPORT2
diff --git a/icu4c/source/common/unicode/uniset.h b/icu4c/source/common/unicode/uniset.h
index 676dea8891ce..0abc75424029 100644
--- a/icu4c/source/common/unicode/uniset.h
+++ b/icu4c/source/common/unicode/uniset.h
@@ -1641,7 +1641,7 @@ class U_COMMON_API UnicodeSet U_FINAL : public UnicodeFilter {
     void applyIntPropertyValue(const UCPMap *map,
                                UCPMapValueFilter *filter, const void *context,
                                UErrorCode &errorCode);
-#endif
+#endif  /* U_HIDE_DRAFT_API */
 
     /**
      * Set the new pattern to cache.
diff --git a/icu4c/source/i18n/unicode/dcfmtsym.h b/icu4c/source/i18n/unicode/dcfmtsym.h
index 737a83c8e8a0..55e3d8a6b3b5 100644
--- a/icu4c/source/i18n/unicode/dcfmtsym.h
+++ b/icu4c/source/i18n/unicode/dcfmtsym.h
@@ -529,7 +529,7 @@ inline const UnicodeString& DecimalFormatSymbols::getConstDigitSymbol(int32_t di
     ENumberFormatSymbol key = static_cast<ENumberFormatSymbol>(kOneDigitSymbol + digit - 1);
     return fSymbols[key];
 }
-#endif
+#endif /* U_HIDE_INTERNAL_API */
 
 // -------------------------------------
 
diff --git a/icu4c/source/i18n/unicode/decimfmt.h b/icu4c/source/i18n/unicode/decimfmt.h
index ba5452f699df..88649f3eebdb 100644
--- a/icu4c/source/i18n/unicode/decimfmt.h
+++ b/icu4c/source/i18n/unicode/decimfmt.h
@@ -2058,7 +2058,7 @@ class U_I18N_API DecimalFormat : public NumberFormat {
     void formatToDecimalQuantity(const Formattable& number, number::impl::DecimalQuantity& output,
                                  UErrorCode& status) const;
 
-#endif
+#endif  /* U_HIDE_INTERNAL_API */
 
 #ifndef U_HIDE_DRAFT_API
     /**
diff --git a/icu4c/source/i18n/unicode/dtptngen.h b/icu4c/source/i18n/unicode/dtptngen.h
index 21173fcc94c0..26ccc64060f1 100644
--- a/icu4c/source/i18n/unicode/dtptngen.h
+++ b/icu4c/source/i18n/unicode/dtptngen.h
@@ -498,27 +498,23 @@ class U_I18N_API DateTimePatternGenerator : public UObject {
 private:
     /**
      * Constructor.
-     * @stable ICU 3.8
      */
     DateTimePatternGenerator(UErrorCode & status);
 
     /**
      * Constructor.
-     * @stable ICU 3.8
      */
     DateTimePatternGenerator(const Locale& locale, UErrorCode & status);
 
     /**
      * Copy constructor.
      * @param other DateTimePatternGenerator to copy
-     * @stable ICU 3.8
      */
     DateTimePatternGenerator(const DateTimePatternGenerator& other);
 
     /**
      * Default assignment operator.
      * @param other DateTimePatternGenerator to copy
-     * @stable ICU 3.8
      */
     DateTimePatternGenerator& operator=(const DateTimePatternGenerator& other);
 
diff --git a/icu4c/source/i18n/unicode/numberformatter.h b/icu4c/source/i18n/unicode/numberformatter.h
index 8a0325167639..469949a2878e 100644
--- a/icu4c/source/i18n/unicode/numberformatter.h
+++ b/icu4c/source/i18n/unicode/numberformatter.h
@@ -2324,7 +2324,7 @@ class U_I18N_API LocalizedNumberFormatter
      */
     int32_t getCallCount() const;
 
-#endif
+#endif  /* U_HIDE_INTERNAL_API */
 
     /**
      * Creates a representation of this LocalizedNumberFormat as an icu::Format, enabling the use
@@ -2390,7 +2390,7 @@ class U_I18N_API LocalizedNumberFormatter
      */
     void formatImpl(impl::UFormattedNumberData *results, UErrorCode &status) const;
 
-#endif
+#endif  /* U_HIDE_INTERNAL_API */
 
     /**
      * Destruct this LocalizedNumberFormatter, cleaning up any memory it might own.
@@ -2592,7 +2592,7 @@ class U_I18N_API FormattedNumber : public UMemory {
      */
     void getAllFieldPositionsImpl(FieldPositionIteratorHandler& fpih, UErrorCode& status) const;
 
-#endif
+#endif  /* U_HIDE_INTERNAL_API */
 
     /**
      * Copying not supported; use move constructor instead.
diff --git a/icu4c/source/i18n/unicode/unumberformatter.h b/icu4c/source/i18n/unicode/unumberformatter.h
index 445af3136d38..5926e0e3a9b8 100644
--- a/icu4c/source/i18n/unicode/unumberformatter.h
+++ b/icu4c/source/i18n/unicode/unumberformatter.h
@@ -253,22 +253,27 @@ typedef enum UNumberGroupingStrategy {
      *
      * @draft ICU 61
      */
-            UNUM_GROUPING_THOUSANDS,
+            UNUM_GROUPING_THOUSANDS
 
+#ifndef U_HIDE_INTERNAL_API
+    ,
     /**
      * One more than the highest UNumberGroupingStrategy value.
      *
      * @internal ICU 62: The numeric value may change over time; see ICU ticket #12420.
      */
             UNUM_GROUPING_COUNT
+#endif  /* U_HIDE_INTERNAL_API */
 
 } UNumberGroupingStrategy;
 
+#ifndef U_HIDE_DEPRECATED_API
 /**
  * Old name for compatibility: will be removed in ICU 64.
  * @deprecated ICU 63
  */
 typedef UNumberGroupingStrategy UGroupingStrategy;
+#endif  /* U_HIDE_DEPRECATED_API */
 
 #endif  /* U_HIDE_DRAFT_API */